JALauncher

Download the launcher to play.

On a Mac: unzip it and open the app. The first time, macOS says it can't check it: open System Settings → Privacy & Security and click Open Anyway (or right-click the app and choose Open).

On Windows: open it. It sets itself up in a few seconds, with a Start menu shortcut, and opens the launcher. If Windows says it protected your PC, click More info, then Run anyway.