Ahoy, according to the rules, ANY engine is allowed. So I made a game according to the motto: "The best game engine is you!:)". Sooo, it's not a computer nor smartphone game, although it can be played THROUGH (NOT JUST ON) computers or smartphones.

Enjoy!:) https://ormrin.itch.io/the-simplest-space-opera

P S. It's a minimalistic TTRPG, so I clicked the category RPG.