[boothby]

I'm quite fond of Pixel Dungeon. It's quite simplistic compared to NetHack but it's good fun (if you like dying early and often) and looks nice. And, bonus, it's GPL3-licensed and hasn't seen an update since 2015, so not only are there a bunch of really creative forks out there, but they're also open source.

[chongli]

Shattered Pixel Dungeon is my favourite fork. The game is actively developed and has done a ton of cool things to change up the formula. Really great game to play on a phone!