Been wondering that after playing Undertale Yellow (great game, btw)

Romhacks would fall into a different category, more like modding the main game.

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[–] 1 point 3 months ago*

Thief. The best fan-made game is The Dark Mod (actually a standalone game; not a mod). There are hundreds of missions of varying quality.

Also, OpenTTD is a free open-source game implementing the concept of Transport Tycoon Deluxe from scratch.

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