>>10
I've made one before, but I won't post it because frankly, it sucked. The cool feature was that there was a sort of half-assed functional engine implemented, so you could do things like take a sword and enchant it so that when you did a thing with it (equip, unequip, swing, hit, miss, etc) a thing would happen to something (you, the monster you were fighting, the world, etc). So, at a basic level, you could enchant your sword to deal fire damage to the target when you connected, but at a higher level there was a proof-of-concept enchantment such that when it hit the monster, it turned whatever they were wearing on their feet into rubber boots and gave the ground the WATERY attribute. That was going to be what was fun about the game: all the effects would be strange, and you'd have to figure out whether "Sword of temporarily summoning eels except on odd numbered levels, when they'd be scorpions" was better than "Lance of possibly restoring your hit points but also possibly turning the ground around you into walls. Also makes opponent switch handedness whenever it hits".
I eventually wanted to bind Guile to it, so at high levels you would primarily interact with the game through writing your own functions as spells from within the game, then casting them, but I couldn't think of a way to do it such that the difficulty would scale nicely. Sure, it would be nice to have a spell that rescinded one of a monster's invulnerabilities, but if you're already fucking around with its internals, why don't you just set the health to -1 and be done with it? Likewise, if you got the ability to rewrite bits of the map, why would you bother setting elaborate flame traps or purifying swamps when you could just make downstairs everywhere?
What sucked about it was that it turns out I can't write content for the life of me (well, I can write interesting effects, but that's about it). So you just traversed an endless series of randomly generated caverns, fighting placeholder creatures, and if you were in the dev version you could go to an altar and modify the internals of your equipment and make them do fire damage or give monsters galoshes or something.