Any game engine is allowed as long as it is playable in-browser. If your game is not playable in-browser, it has to be one of the formats in the accepted list of formats. The reason games must be from the formats below is to allow for the most people possible to be able to play your game on tablets, phones, computers, and what-have-you.
Accepted formats:
.bin (Atari only), .nes, .sfc, .smc, .md, .gb, .gbc, .gba or .nds
WARNING:
If your game is not free, it must be playable in-browser or you will be disqualified from the game jam.