This a OS Runescape launcher for Linux systems using snaps (Snapcraft)
The snap only holds the environment to run a java application.
When started it will download the launcher which downloads the Windows installer from Jagex and extract the game. Since it's java based, the game will run normally inside the snap keeping your system safe.
Old School Runescape for Linux, OSRS Linux, OSRS snapcraft, Old School Runescape snap