XDA’s piece this week made a point every Pi tinkerer already suspected: most single-board-computer projects never come close to using the RAM on a modern Pi. An 8 GB Pi 5 runs Pi-hole at 40 megabytes resident. That is not a case for buying less RAM. That is a case for putting the extra RAM to work on a second project on the same board, or for keeping the older 1 GB and 2 GB Pis useful long after the new hardware ships.
We tested 7 apps that comfortably run on a Pi Zero 2 W, a 1 GB Pi 3, or a 2 GB Pi 4, so you know where the low-RAM ceiling is before you commit hardware. Each pick below has a real memory footprint under 200 MB in normal operation, works headless, and is stable enough to leave on a shelf for months. All seven install on the popular desktop OSes too (Raspberry Pi OS is Debian; the same packages ship for Windows via WSL, macOS via Homebrew, and any Linux distro).
What to look for in a low-RAM Pi app
- Idle RAM under 150 MB so a Pi Zero 2 W with 512 MB usable stays healthy.
- Runs headless with a web UI, not a desktop-only GUI, so the board can go in a cupboard.
- Read-mostly disk activity to spare a MicroSD from write-wear.
- Sensible defaults, ideally a single-command install.
- Active maintenance. Abandoned services turn into unpatched attack surface fast.
- Runs in Docker as an option, so the same app can co-exist with a second project on a bigger Pi.
Quick comparison
| App | Best for | Idle RAM | Free | Open source |
|---|---|---|---|---|
| Pi-hole | Network-wide DNS ad blocking | ~40 MB | Yes | Yes |
| Home Assistant Core | Smart-home hub without the OS overhead | ~150 MB | Yes | Yes |
| Mosquitto | MQTT broker for IoT projects | ~5 MB | Yes | Yes |
| MotionEye | Multi-camera CCTV | ~120 MB | Yes | Yes |
| Syncthing | Peer-to-peer file sync | ~70 MB | Yes | Yes |
| OctoPrint | 3D printer web control | ~100 MB | Yes | Yes |
| AdGuard Home | DNS ad blocking with a friendlier UI | ~70 MB | Yes | Yes |
The 7 best low-RAM Raspberry Pi project apps
1. Pi-hole, best network ad blocker
Pi-hole is the canonical light Pi project. It runs as a local DNS resolver that drops requests to known ad and tracker domains. Idle RAM sits at about 40 MB, disk writes are negligible if you disable long-term query logging, and a Pi Zero 2 W keeps up with a household network without breaking a sweat.
Where it falls short: Setting Pi-hole as the network’s DNS requires a router change most ISP routers do not make easy. Some sites lean hard on the blocked domains and break.
Pricing:
- Free: Full app.
- Paid: Free.
Platforms: Linux (Raspberry Pi OS is canonical), Docker on Windows and macOS.
Download: Pi-hole
Bottom line: The first project a Pi should do. The lowest RAM footprint of anything on this list.
2. Home Assistant Core, best low-RAM smart-home hub
Home Assistant Core is the Python-only build without the full supervised OS. It uses about 150 MB idle on a Pi 3 with a modest integration set (a dozen sensors, a hub, a few automations). The trade-off versus the full Home Assistant OS is that add-ons are not managed for you; you install them as separate services or containers.
Where it falls short: Core alone does not include the Add-on Store, so integrations like ESPHome or Zigbee2MQTT run as their own systemd services.
Pricing:
- Free: Full app.
- Paid: Free.
Platforms: Linux (Raspberry Pi OS, Debian, Ubuntu), Docker on Windows and macOS.
Download: Home Assistant Core install
Bottom line: The pick when the full HA OS feels heavy and you want smart-home automation on an older Pi.
3. Mosquitto, best MQTT broker
Mosquitto is the reference MQTT broker for IoT projects and is genuinely tiny. Under 5 MB resident on a Pi Zero, handles hundreds of clients on a Pi 3, and does not care what OS the clients run. If you build Home Assistant, ESPHome, Zigbee2MQTT, or Node-RED, this is the message bus.
Where it falls short: No built-in web UI. You configure via a text file and use a client to inspect topics.
Pricing:
- Free: Full app.
- Paid: Free.
Platforms: Linux, Windows, macOS.
Download: Mosquitto
Bottom line: Install this on every Pi that talks to a sensor. Nothing else on this list uses less RAM.
4. MotionEye, best DIY camera server
MotionEye turns a Pi with USB or CSI cameras into a small NVR. Web UI, motion detection, recording, and time-lapse. It sips RAM at idle and only pushes CPU when motion detection fires. A Pi 3 handles two 720p streams without stress; a Pi 4 with a couple GB handles four.
Where it falls short: Modern H.264 recording still stresses SD cards. Use a USB SSD or network share for storage if the cameras record more than motion clips.
Pricing:
- Free: Full app.
- Paid: Free.
Platforms: Linux (Raspberry Pi OS), Docker on Windows and macOS.
Download: MotionEye
Bottom line: The lowest-cost way to turn a spare Pi into a two-camera CCTV.
5. Syncthing, best peer-to-peer file sync
Syncthing is the Dropbox-shaped file sync app that does not use a central server. Point two devices at each other and shared folders stay synced. About 70 MB idle on a Pi, so a Pi Zero 2 W can act as an always-on sync target for a laptop and a phone. No cloud account, no vendor lock-in.
Where it falls short: Discovery on some restrictive networks fails without a small relay hop. NAT-traversal is generally fine but not perfect.
Pricing:
- Free: Full app.
- Paid: Free.
Platforms: Windows, macOS, Linux (including Raspberry Pi OS).
Download: Syncthing
Bottom line: The pick for a private sync target. Add an external drive to the Pi and forget about it.
6. OctoPrint, best 3D printer host
OctoPrint turns a Pi into the front end for a 3D printer, with a web UI, live camera view, temperature charts, and a plugin ecosystem. About 100 MB idle. A Pi Zero 2 W hosts it happily for a single printer at 720p camera. Move to a Pi 4 if you add multiple cameras and heavy plugins.
Where it falls short: Streaming a full 1080p camera view on a Pi Zero taxes CPU. Slicing on the Pi is not really viable; slice on the desktop and upload gcode.
Pricing:
- Free: Full app.
- Paid: Free (optional donations).
Platforms: Linux (Raspberry Pi OS is canonical), Docker on Windows and macOS.
Download: OctoPrint
Bottom line: The 3D-printer project the Pi was practically made for. Under 150 MB total on a headless install.
7. AdGuard Home, best friendly DNS blocker
AdGuard Home does the same job as Pi-hole with a more modern UI, per-client rules, and a slightly higher RAM footprint. Around 70 MB idle. If Pi-hole feels dated to configure, AdGuard Home is the drop-in replacement with a cleaner dashboard.
Where it falls short: Slightly higher memory use than Pi-hole. Community blocklists are the same, so blocking quality is similar.
Pricing:
- Free: Full app.
- Paid: Free.
Platforms: Linux (Raspberry Pi OS), Windows, macOS.
Download: AdGuard Home
Bottom line: Pick this if you want a nicer UI and per-device controls over the older Pi-hole dashboard.
How to pick the right one
If you have a Pi Zero 2 W and want it to earn its keep, install Pi-hole and Mosquitto together. Both fit in 100 MB combined.
If your household includes at least one 3D printer, dedicate a Pi 3 to OctoPrint with MotionEye running on the same board for the camera view.
If you want a smart home hub on an older Pi, install Home Assistant Core and skip the full HA OS overhead.
If you have a spare USB drive, add Syncthing to any Pi already on the network. It becomes your private backup target for free.
If you already run Pi-hole and are considering the swap, install AdGuard Home on a second Pi first and A/B them for a week before committing.
FAQ
How much RAM does a Raspberry Pi Zero 2 W actually have?
512 MB total. About 400 MB is usable after the OS. Every app on this list runs on a Zero 2 W individually; you can also run two or three of them at once.
Do these apps run on Ubuntu on a Pi?
Yes. All seven are packaged for Debian, Ubuntu, and Raspberry Pi OS. Most also ship a Docker image if you prefer container isolation.
Can I run more than one of these on the same Pi?
Absolutely. Pi-hole, Mosquitto, Syncthing, and Home Assistant Core happily share a Pi 4. Add OctoPrint or MotionEye only if the Pi is dedicated to a printer or camera.
What is better than an SD card for storage?
A USB SSD or a small NVMe hat. SD cards wear out under log-heavy workloads and are the most common cause of Pi failure. Any of the apps above will happily run from a USB-attached SSD.
Are these apps safe to expose to the internet?
Pi-hole and AdGuard Home stay on the LAN. Home Assistant, Syncthing, and OctoPrint are safest behind a reverse proxy with authentication or a Tailscale-style overlay network. Exposing them raw on port 80/443 is a well-known bad idea.
