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(+1)

Sorry to take so long to respond - no "engine" in the colloquial sense, I develop using GM Studio 1.4 as a code and resource management IDE - LLTA uses a LOT of the GMS built-in systems (part of why it runs.... not great in places lol), but since then i've programmed each project's gameplay, core loops, and visual presentation from scratch. i always want to promote mostly-from-scratch development since it leads to more elemental, focused, and disciplined game design, but if you're like me and don't have the time or budget to go 100% "c# in notepad" mode, as an IDE to work in and handle low-level stuff I definitely recommend GMS over bloated systems like Unity. (can't speak for GMS2 tho, haven't used it myself)