JSystem is the in-house framework that Nintendo used for first-party GameCube and Wii games. It has libraries to assist with 3D and 2D Graphics, Audio, Maps, Effects, Core Management, and has Support and Utility Classes.
The earliest confirmed title that uses it is Luigi's Mansion (2001) for GameCube, the last being The Legend of Zelda: Skyward Sword (2011) for Wii.
It was created for more efficient game development, containing a set of libraries to do so. It was still an early development project by workers of Nintendo EAD during the development of the GameCube, where the GameCube IPL uses a very early version of Jaudio for Audio.
The development of JSystem was finished when the Nintendo DS came out, and it kept being used for most of the first-party Nintendo games, until they slowly transitioned over to NintendoWare for Revolution(Wii) (NW4R). Newer versions of NintendoWare are still used for the newest games today.
JSystem keeps seeing changes with each game and not all games use all libraries of it, so we started a google sheets here to document which games use what library.