Best Nethack

xNetHack is a NetHack variant by aosdict, based on NetHack 5.0 development, noted for balance fixes and reduced tedium rather than added bulk.

Slash'EM is a NetHack variant begun by Warren Cheung in 1997, notable for adding classes, monsters and features later echoed in NetHack.

EvilHack is Keith Simpson's NetHack 3.6.2-based variant, begun in 2018 and released on Hardfought in 2019, with new races, roles and branches.

FIQHack is a NetHack 4-based NetHack variant focused on monster AI, balance and interface changes, with public play on Hardfought servers.

NetHack Fourk is a NetHack 4-based variant that makes experimental but restrained gameplay changes, including new races such as sylphs and scurriers.

notdNetHack is a dNetHack variant that rebalances its parent while adding content such as salamander and ent races and the Illithanachronounbinder role.

Slash'EM Extended is a 2014 NetHack-family variant by Amy Bluescreenofdeath, notable for greatly expanding Slash'EM's roles, monsters and rules.