I'm not 100% sure, but I want to join, but I don't know I know any of allowed engines.

From the rules on the jam page: 

"Any game engine is allowed as long as you can set your game's resolution to 84 x 48 or limit the number of pixels the player sees to 84 x 48. It must also be able to use the provided palette. Pico-8 devs click here to see how you can participate!"