Same files.
More disk.

a0 compresses the stuff you haven't opened in a week and unpacks it the second you do. Nothing moves, nothing gets renamed, no new folder to remember. Your files just take less space.

curl -fsSL https://a0.0a0.dev/install.sh | sh

Linux on x86_64 or 64-bit ARM. Arch, Debian, Ubuntu, Mint, Fedora, openSUSE, Alpine. Installs nothing else and compresses nothing until you tell it which folders.

One laptop, two days in

282 GBdisk space back

61%smaller on average

162,386files compressed

130 GBof duplicates, stored once

Untouched files, 463.5 GBnow 181.8 GB

A 1 TB laptop with a 710 GB home folder: games, an Unreal project, Java builds, old backups. Everything except keys and container images. 130 GB of it turned out to be duplicate data, which is stored once.

Where it came from

Unreal Engine game project79.3 → 19.6 GB
Steam library81.8 → 38.4 GB
Minecraft client mod, builds and Gradle37.4 → 5.3 GB
Old backups46.3 → 17.1 GB
Portfolio and design files23.8 → 1.8 GB
Roblox via Vinegar (Flatpak)17.7 → 1.2 GB
Motion design project12.1 → 0.1 GB
Gradle cache10.4 → 2.8 GB

By file type

Zip archives .zip60.6 → 21.7 GB
PNG images .png36.7 → 0.6 GB
Windows DLLs (Proton games) .dll26.3 → 4.0 GB
Unreal assets .uasset21.8 → 1.8 GB
Object files and static libs .o .a34.7 → 5.0 GB
Debug symbols .pdb20.1 → 3.6 GB
Linux shared libraries .so21.7 → 5.3 GB
Logs .log15.2 → 0.8 GB

Already-compressed formats get one test run and are kept only if they shrink by 10% or more. Plenty of zips are stored without compression, and PNGs repeat across projects.

Speed

Compressing, in the background16 of 32 threads, lowest CPU and disk priority	190 MB/s
Opening a compressed 440 MB filethe program waits this long once, then it's a normal file again	0.6 s
Opening a compressed 2 GB file, cold cachethe same file uncompressed reads in 1.1 s	2.3 s
Pausing it`a0 pause` stops a running scan	under 1 s
Protected again after a restart162,386 compressed files re-armed	0.24 s
Daemon memory when idle	~10 MB

Tested on

InstallerDebian 12, Ubuntu 20.04 and 24.04, Fedora 41, Arch, Alpine, openSUSE Tumbleweed	7 / 7
Filesystemsext4, btrfs, xfs, and inside the hardened systemd sandbox	4 × 61 checks
Crash, power cut, file opened mid-compressionreaders racing the compressor for 20 s never saw wrong data	0 wrong reads

How it works

Every few hours a0 looks for files nobody touched in 7 days. Over a megabyte, not already compressed, not in your config or keys.
It packs them into one shared store and leaves the file where it was. Same name, same size, same date. It just doesn't take up blocks anymore.
When any program opens one, Linux pauses that program while a0 unpacks it. Usually under a second. Then the program carries on and never knows.

render.pak  2.0 GB   on disk 2.0 GB
      │  untouched for 7 days
      ▼
render.pak  2.0 GB   on disk 0 B      store +716 MB
      │  something opens it
      ▼
render.pak  2.0 GB   on disk 2.0 GB   ~1.4 s later

Before you install

The a0 service has to be running. It starts before you log in. If you stop it, compressed files read as empty until it's back — a0 status tells you.
First launch of a compressed game is slower, roughly a second per GB. After that it's a normal file again until it sits unused for another week.
It refuses to compress anything that's open, checks every block before freeing space, and survives crashes and power cuts mid-way.
Undo is one command: sudo a0 thaw-all puts every file back, even with the service stopped.
It uses half your CPU threads, at the lowest priority. a0 speed changes that, a0 pause 2h stops it for a while.
Container and VM images are never touched (Docker, Podman, LXC, Waydroid), whatever the config says.
Needs a normal desktop kernel (fanotify permission events — Arch, Ubuntu, Fedora, Debian all ship it) and ext4, xfs or btrfs.

After installing

a0 estimate ~: How much you'd get back. Reads only, changes nothing.
sudoedit /etc/a0/config.toml: Pick folders. Or install with --home to start with your home folder.
sudo a0 scan --dry-run: The exact list it would compress.
a0 status: How much it saved.
a0 pause 2h: Leave the CPU alone for a while. a0 resume picks up where it stopped.
a0 speed 4: How many threads it may use. Default: one per core.
sudo a0 thaw-all: Everything back to normal.

Home folder straight away:

curl -fsSL https://a0.0a0.dev/install.sh | sh -s -- --home

Remove it (unpacks everything first):

curl -fsSL https://a0.0a0.dev/install.sh | sh -s -- --uninstall

Same files.More disk.