The NetHack4 developers write about their fork of the NetHack roguelike, covering C programming, save systems, game design and terminal palettes.
HN commenters point to it as the fork made when official NetHack development stalled, and recommend it for its interface and usability improvements.
They cover that in the FAQ: http://nethack4.org/faq.html
Basically, NetHack development stalled out, so the developer(s?) behind NetHack 4 decided to fork it. Unlike other forks whose main goal is to put cool stuff in the game without regard for taste or balance, they wanted to stay true to the original.
Not that I agree with the fork name. It's best to not call your fork something that could be confused with the original, were the original devs to ever reach a 4.0 release.
Personally, since I'm less interested in MS-DOS modes and fixed-length 8bit charset modes, I switched to the redesigned NetHack 4, which works fine with modern UTF-8 terminals.
NetHack 4 is geared towards progression of the game and staying up to date with the changing world rather than mothballing the old game. It's a separate project from NetHack 3.x, with different goals and development teams.
http://nethack4.org
The DevTeam released nethack-3.4.3 in Dec 2003, and then pretty much went dormant for 11 years -- no new releases, no roadmap, nothing. So some time around 2013 some people not connected to the DevTeam created this project: http://nethack4.org/ . So now the DevTeam skips 4.x version numbers completely to avoid confusion.
Possibly to avoid conflicts with Nethack4[0], which was a fork of the Nethack 3.x series back when development was stalled. I think the guy behind it later joined the main Nethack dev team.
[0] http://nethack4.org/
I wouldn't said it's inherently bad game design, different people have different preferences. Here's a good blog post discussing such decisions.
http://nethack4.org/blog/strategy-headroom.html
There are a lot of variations of NetHack, among them the official successor project, Nethack4[1]. One of its goals is to have a better interface.
[1]: http://nethack4.org/