Microsoft’s official support for Office 2021 ends on October 13, 2026. After that date, no more security patches, no more bug fixes, no more extended security updates from Redmond. The apps will keep opening, but every new CVE that surfaces in Word, Excel or Outlook stays open forever on those installs. That is the legacy Office security problem, and it lands hard on small businesses, schools and home users who bought a perpetual license precisely to avoid the 365 subscription.
There are two workable answers. Keep the old install and pay a third party to patch it, which is what 0patch does with in-memory micropatches that need no reboot. Or move to a free suite that reads and writes DOCX, XLSX and PPTX cleanly and gets security updates on the normal cadence. Below are seven tools worth looking at, ordered from patch-in-place to full replacement.
What to look for in a legacy Office security option
Five things matter when you evaluate this shortlist.
Patch in place vs replace. 0patch keeps your existing Office binaries and applies fixes at runtime. Everything else on this list is a replacement suite, so you also swap the file associations, the ribbon and the muscle memory.
Format fidelity. Complex DOCX with tracked changes, XLSX with pivot tables and macros, PPTX with SmartArt: how much of that survives a round trip. Open-source suites have closed most of the gap, but complex templates and macro-heavy spreadsheets still bite.
Macro handling. VBA macros are a common infection vector and a common workflow crutch. Some suites run a subset, some run none, and 0patch keeps VBA behaviour identical while patching the underlying flaws.
Support timeline. How long the vendor commits to security updates on the version you install. For a legacy scenario this is the whole point.
Licensing cost. Free forever, one-time purchase, annual subscription or per-seat enterprise. Legacy Office buyers usually chose perpetual for a reason, so this matters.
Quick comparison
| App | Best for | Free plan | Starting price | Support horizon |
|---|---|---|---|---|
| 0patch Agent | Keeping Office 2021 running | Free tier for older CVEs | Around 25 euros per user, per year | Announced through late 2029 |
| LibreOffice | Full replacement, community-run | Yes, MPL 2.0 | Free | Ongoing, quarterly releases |
| OnlyOffice Desktop | Best MS Office look and feel | Yes, AGPL 3.0 | Paid tiers for cloud add-ons | Ongoing |
| SoftMaker FreeOffice | Lightweight Windows replacement | Yes | Around 30 euros for paid Office | Ongoing |
| WPS Office | Familiar ribbon plus PDF tools | Yes, ad-supported | Around 3 dollars per month | Ongoing |
| Collabora Office | Business-grade LibreOffice | Yes, community build | Per-user annual subscription | Long-term support branches |
| Nextcloud Office | Team collaboration on your server | Yes with self-hosting | Enterprise per-seat | Tied to Nextcloud releases |
The apps
#1. 0patch Agent, Best for keeping Office 2021 exactly as it is
0patch is the only tool here that treats the legacy Office security problem as a patching problem instead of a migration problem. The agent runs in the background, watches which processes launch, and injects tiny in-memory fixes for known vulnerabilities without touching the original binaries. Files on disk stay signed, no reboot is needed, and VBA and add-ins keep working the way they always did. The company has committed to critical Office 2021 micropatches through at least late 2029, with an extension possible if demand holds.
Where it falls short: micropatches cover critical vulnerabilities, not every low-severity issue, and you rely on one vendor’s triage priorities. If that vendor sunsets the product, you are back on unpatched Office.
Pricing:
- Free: a free tier covers some older 0-days and legacy Windows fixes
- Paid: 0patch Pro is around 25 euros per user per year, Enterprise around 35 euros per seat per year
Platforms: Windows
Download: Publisher site at https://0patch.com
Bottom line: if changing document tools is off the table, this is the cheapest way to keep an Office 2021 fleet defensible for three more years.
#2. LibreOffice, Best for a full free replacement
LibreOffice is the reference open-source office suite, maintained by The Document Foundation and shipped under the MPL 2.0. Writer, Calc, Impress, Draw, Base and Math cover everything the Microsoft suite does, and DOCX, XLSX and PPTX are treated as first-class formats rather than imports. Two release trains ship in parallel, a Fresh line with new features and a Still line for conservative deployments, both patched on a predictable quarterly cadence.
Where it falls short: complex XLSX with heavy conditional formatting and pivot tables can drift, and VBA macros run through a compatibility layer that does not cover every case.
Pricing:
- Free: full suite for personal and commercial use
- Paid: none, though Collabora and other vendors sell supported builds
Platforms: Windows, macOS, Linux
Download: Publisher site at https://www.libreoffice.org
Bottom line: the safe default replacement, free forever, with the largest community and the longest track record.
#3. OnlyOffice Desktop, Best for a Microsoft-style interface
OnlyOffice took a different bet from LibreOffice: build the editors around DOCX, XLSX and PPTX natively, and ship a ribbon UI that Office users can pick up in minutes. The desktop editors are free and open source under AGPL 3.0, they open PDFs and PDF forms, and they connect to any WOPI-compatible cloud, including OnlyOffice DocSpace, Nextcloud and ownCloud.
Where it falls short: collaboration features assume you connect to a document server, and the ODF support, while present, is weaker than LibreOffice’s.
Pricing:
- Free: full desktop suite for home and commercial use
- Paid: DocSpace and Enterprise plans for team and cloud features
Platforms: Windows, macOS, Linux
Download: Publisher site at https://www.onlyoffice.com
Bottom line: the closest look and feel to the Office ribbon, with the best out-of-the-box DOCX and XLSX fidelity in the open-source category.
#4. SoftMaker FreeOffice, Best for a fast, lightweight Windows install
FreeOffice is the ad-free freeware cut of SoftMaker Office. TextMaker, PlanMaker and Presentations open and save native DOCX, XLSX and PPTX, the installer is small, and startup times on older hardware are noticeably faster than either LibreOffice or the Microsoft original. The developer, SoftMaker, is a German software house that has been shipping office suites since the 1980s and updates FreeOffice on a steady cadence.
Where it falls short: no macro support in the free build, and some advanced formatting features are gated to the paid SoftMaker Office release.
Pricing:
- Free: full FreeOffice suite for personal and commercial use
- Paid: SoftMaker Office starts around 30 euros for a one-time license or an annual NX subscription
Platforms: Windows, macOS, Linux
Download: Publisher site at https://www.freeoffice.com
Bottom line: the pick for an old ThinkPad or a small-footprint Windows VM where every startup second counts.
#5. WPS Office, Best for PDF-heavy workflows
WPS Office bundles Writer, Spreadsheets, Presentation and a genuinely strong PDF editor into a single ribbon UI that mirrors Microsoft’s layout very closely. The free tier is ad-supported, and the paid Premium tier removes ads and unlocks cloud sync, template libraries and AI features. Its MS Office format compatibility is high, and multi-tab document editing is a small quality-of-life feature the others do not match.
Where it falls short: the free version shows ads, and past versions have shipped with data-collection defaults that home users may want to review before installing.
Pricing:
- Free: full suite with ads
- Paid: WPS Premium starts at around 3 dollars per month
Platforms: Windows, macOS, Linux, Android, iOS
Download: Publisher site at https://www.wps.com
Bottom line: a solid Office replacement if you edit PDFs as often as documents, with a very familiar ribbon.
#6. Collabora Office, Best for supported LibreOffice in a business
Collabora Office is the commercially supported build of LibreOffice, maintained by Collabora Productivity, one of the largest code contributors to the upstream project. You get long-term support branches, security backports on a defined schedule, and a support contract you can point an auditor at. The desktop client is available for Windows, macOS and Linux and pairs with Collabora Online for browser editing.
Where it falls short: the community desktop build is free, but production support and long-term branches are subscription-only.
Pricing:
- Free: Collabora Office community build for evaluation
- Paid: per-user annual subscription, usually via reseller
Platforms: Windows, macOS, Linux
Download: Publisher site at https://www.collaboraonline.com
Bottom line: LibreOffice with an SLA. If a compliance team needs a phone number to call when a CVE lands, this is the pick.
#7. Nextcloud Office, Best for self-hosted team editing
Nextcloud Office is Collabora Online, packaged as an app inside Nextcloud so a team can edit DOCX, XLSX and PPTX together in the browser, on your own server, with the files never leaving your storage. For a small office replacing a legacy Office plus a file share, this replaces both at once and gives you end-to-end encryption on the storage layer as well.
Where it falls short: you need to run a Nextcloud instance, so the total cost includes a server or a managed host, and desktop editing is browser-based rather than a native client.
Pricing:
- Free: self-hosted with the community Collabora Online Development Edition
- Paid: Nextcloud Enterprise per-seat annual pricing
Platforms: Browser client on Windows, macOS, Linux (server on Linux)
Download: Publisher site at https://nextcloud.com/collabora
Bottom line: the pick if you want to retire the file server, the Office install and the third-party sharing tool at once.
How to pick the right one
Match the tool to the constraint you cannot bend.
If you cannot touch document formats or macros, and the workflow depends on Word and Excel behaving exactly the way they always have, run 0patch Agent on top of Office 2021 and buy yourself three more years to plan a migration. This is the only option here that keeps the original binaries.
If you want to move off entirely and cost is the driver, LibreOffice is the default. Pick OnlyOffice Desktop instead when the users push back on the LibreOffice UI and would rather see a ribbon they recognise.
If startup speed on aging hardware matters more than macro support, SoftMaker FreeOffice is faster and lighter than either. If PDF editing is a daily task, WPS Office bundles both.
If the deployment is a business that needs a support contract and a security SLA, Collabora Office is LibreOffice with a phone number attached. If you also want to retire a file server and give the team browser-based collaborative editing, Nextcloud Office plus a self-hosted Nextcloud instance handles storage, sharing and editing in one stack.
For most home users leaving Office 2021 behind in 2026, the honest answer is LibreOffice for personal work and 0patch for the machine that still runs one XLSX nobody has time to port.
FAQ
When does Office 2021 support end? Microsoft ends mainstream support for Office LTSC 2021 on October 13, 2026. There are no extended security updates from Microsoft after that date, so any new CVE stays open unless you patch it through another route.
Is 0patch legal and safe? Yes. 0patch is a Slovenian security company that has been shipping micropatches for end-of-life Windows and Office versions for years. The patches are applied in memory to running processes and do not modify Microsoft’s binaries on disk, so they do not violate Office licensing terms.
Can LibreOffice really open my old DOCX and XLSX files? Almost always, yes. Plain documents and typical spreadsheets round-trip cleanly. Where it gets messy is complex templates with heavy tracked changes, VBA-heavy macros, or Excel workbooks with pivot tables and slicers. Test the files you actually care about before you commit.
What happens to Outlook if I stop using Office? None of the suites on this list ship a full Outlook replacement. Common paths are Thunderbird for POP or IMAP mail, the built-in Windows Mail app for small setups, or a browser tab for hosted mailboxes. For Exchange or Microsoft 365 mailboxes, Outlook on the web works in any browser.
Is Office 2019 or Office 2016 covered by 0patch too? Older Microsoft Office versions are already covered by 0patch’s Office micropatch program. Check the vendor’s help centre for the exact list of supported builds and CVEs before you deploy.