Download from mortar.rethunk.tech/download, or every file from Releases.

Windows

Installer: mortar-amd64-installer.exe (mortar-arm64-installer.exe on an ARM PC). It installs for your account only, into %LOCALAPPDATA%\Programs\Mortar, with Start Menu and Desktop shortcuts and no administrator prompt.
Bare program: mortar-windows-amd64.exe or mortar-windows-arm64.exe, run from any folder.
Scoop: scoop bucket add mortar https://github.com/Rethunk-Tech/scoop-bucket, then scoop install mortar/mortar. Scoop handles updates; Mortar's own updater stays off.

The window needs Microsoft's WebView2 Runtime; the installer adds it when missing and the bare program asks first. The builds are not code-signed, so SmartScreen warns the first time: choose More info, then Run anyway.

Linux

AppImage (mortar-linux-x86_64.AppImage, mortar-linux-aarch64.AppImage): chmod +x and run it. It needs glibc 2.35 or newer (Ubuntu 22.04, Linux Mint 21, Debian 12, Fedora 36); on an older system use the Flatpak.
Portable program (mortar-linux-amd64, mortar-linux-arm64): the same requirements plus GTK 3 and WebKitGTK 4.1 (libwebkit2gtk-4.1-0 on Debian and Ubuntu, webkit2gtk4.1 on Fedora, webkit2gtk-4.1 on Arch). It updates itself and on first run adds a menu entry and takes nxm:// links.
Flatpak: flatpak install --user https://mortar.rethunk.tech/packages/flatpak/tech.rethunk.Mortar.flatpakref adds Mortar's signed repository, so flatpak update keeps it current. Each release also has mortar-linux-x86_64.flatpak and mortar-linux-aarch64.flatpak for a one-time install without updates. Sandbox limits:
- Folders outside the Flatpak's allowed set (Steam, Heroic, Lutris and the usual game folders) are invisible. Grant one with flatpak override --user --filesystem=<folder> tech.rethunk.Mortar.
- Add this profile to Steam is refused; the error shows the flatpak run tech.rethunk.Mortar --play=<game>/<profile> --steam-session command to use instead.
- Flatpak Steam cannot read profiles until you choose Grant access in the game's settings.
Homebrew: brew install rethunk-tech/tap/mortar installs the AppImage; brew upgrade updates it.
.deb, .rpm, Arch package: sudo apt install ./mortar_*_amd64.deb, sudo dnf install ./mortar-*.rpm or sudo pacman -U mortar-*.pkg.tar.zst. These do not update themselves; add the repository below.

Linux package repository

Installed from the repository, Mortar updates with the rest of your system (Settings › Updates says "Updated by your package manager"). The signing key is "Mortar packages [email protected]", fingerprint D8B1 C4C2 05C5 FB36 33CB 8B99 00B7 5959 B637 DCB5.

Debian and Ubuntu (amd64, arm64):

sudo apt update && sudo apt install curl
sudo curl -fsSLo /usr/share/keyrings/mortar-archive-keyring.gpg https://mortar.rethunk.tech/packages/mortar-archive-keyring.gpg
sudo curl -fsSLo /etc/apt/sources.list.d/mortar.list https://mortar.rethunk.tech/packages/mortar.list
sudo apt update && sudo apt install mortar

Fedora (x86_64, aarch64); dnf asks once to import the key, so compare its fingerprint with the one above:

sudo curl -fsSLo /etc/yum.repos.d/mortar.repo https://mortar.rethunk.tech/packages/mortar.repo
sudo dnf install mortar

Arch (x86_64, aarch64):

curl -fsSL https://mortar.rethunk.tech/packages/mortar-archive-keyring.asc | sudo pacman-key --add -
sudo pacman-key --lsign-key D8B1C4C205C5FB3633CB8B9900B75959B637DCB5
curl -fsSL https://mortar.rethunk.tech/packages/pacman.conf | sudo tee -a /etc/pacman.conf
sudo pacman -Syu mortar