The installers for the current release, straight from GitHub. Not sure which one? On Windows and Linux it is almost always the first. On a Mac, choose Apple silicon for an M1 or newer. A Raspberry Pi 3, 4 or 5 with the 64-bit Raspberry Pi OS runs OSCAR too, and can sit in the rack as the installation's server.
This is OSCAR 2.1.0. All releases, and what changed.
The first time you open it
Windows
Windows may show "Windows protected your PC", because OSCAR is not signed with a paid certificate. Choose More info, then Run anyway. Allow it through the firewall when asked, or tablets on your network will not reach it.
macOS
macOS may say the developer cannot be verified. Open System Settings > Privacy & Security, scroll down, and choose Open Anyway. You only do this once.
Linux
For the AppImage, make the file executable (chmod +x OSCAR-*.AppImage) and run it. MIDI needs ALSA, which desktop distributions have.
Next
Getting started walks through a first project. OSCAR is open source under the BSD 3-Clause licence: the source is on GitHub.