There is only one file type that uses the .LK12 extension:
LIKO-12 Disk File
An LK12 file contains a LIKO-12 game "cartridge," which can be played with the LIKO-12 virtual fantasy gaming console. The file is saved in the LIKO-12 disk image format and stores all the game data, which includes sprites, tiles, and audio data.
LIKO-12 is one of several fantasy gaming consoles that create retro-style video games, along with TIC-80 and PICO-8. The program is open source and can create games that can be shared with and played by other gamers.
NOTE: LK12 game files can be open and run in LIKO-12 in Windows, macOS, Linux, and Android.
Updated: October 24, 2019