The language of PICO-8 is Lua. The PICO-8 software itself comes with a sprite and map editor, code editor, and the ability to build "cartridges" for distribution. Cartridge code is encoded into a PNG file in the last 3 bytes of every pixel. The Lexaloffle website runs cartridges in the browser when distributed via their forum.
Picolove [https://github.com/picolove/picolove PICOLOVE] is an open-source project emulating the PICO-8 in Love2D, a graphical Lua framework.
[https://www.lexaloffle.com/pico-8.php Lexaloffle website]