From the I-believe-it-not department:
After a 10+ year hiatus, the NetHack DevTeam is happy to announce the release of NetHack 3.6, a combination of the old and the new.
Unlike previous releases, which focused on the general game fixes, this release consists of a series of foundational changes in the team, underlying infrastructure and changes to the approach to game development.
Those of you expecting a huge raft of new features will probably be disappointed. Although we have included a number of new features, the focus of this release was to get the foundation established so that we can build on it going forward.
Read the whole announcement. It's been about twelve years; I honestly hadn't thought we'd see a new release, much less changes to the development process to make it more robust, more open, and generally better.
I was wrong. Break out the crayons and color me tickled pink!
EDIT, 2015-12-09: the updated guidebook offers some more information on Nethack's recent development history:
The release of NetHack 3.4.3 in December 2003 marked the beginning of a long release hiatus. 3.4.3 proved to be a remarkably stable version that provided continued enjoyment by the community for more than a decade. The devteam slowly and quietly continued to work on the game behind the scenes during the tenure of 3.4.3. It was during that same period that several new variants emerged within the NetHack community. Notably sporkhack by Derek S. Ray, unnethack by Patric Mueller, nitrohack and its successors originally by Daniel Thaler and then by Alex Smith, and Dynahack by Tung Nguyen. Some of those variants continue to be developed, maintained, and enjoyed by the community to this day.
At the beginning of development for what would eventually get released as 3.6.0, the development team consisted of Warwick Allison, Michael Allison, Ken Arromdee, David Cohrs, Jessie Collet, Ken Lorber, Dean Luick, Pat Rankin, Mike Stephenson, Janet Walz, and Paul Winner. Leading up to the release of 3.6.0 in early 2015, new members Sean Hunt, Pasi Kallinen, and Derek S. Ray joined the NetHack development team.
In September 2014, an interim snapshot of the code under development was released publicly by other parties. Since that code was a work-in-progress and had not gone through the process of debugging it as a suitable release, it was decided that the version numbers present on that code snapshot would be retired and never used in an official NetHack release. An announcement was posted on the devteam’s official nethack.org website to that effect, stating that there would never be a 3.4.4, 3.5, or 3.5.0 official release version.
In November 2014, preparation began for the release of NetHack 3.6. The 3.6 version merges work done by the development team since the previous release with some of the beloved community patches. Many bugs were fixed and a large amount of code was restructured.
The development team, as well as Steve VanDevender and Kevin Smolkowski ensured that NetHack 3.6.0 continued to operate on various Unix flavors and maintained the X11 interface.
Ken Lorber, Haoyang Wang, Pat Rankin, and Dean Luick maintained the port of NetHack 3.6.0 for Mac.
Michael Allison, Derek S. Ray, Yitzhak Sapir, Alex Kompel, and Dion Nicolaas maintained the port of NetHack 3.6.0 for Microsoft Windows.