Cthangband is an Angband variant written by Dean Anderson and set in H.P. Lovecraft's Dreamlands. Some of the new features of Cthangband include new races, classes, magic systems, and a wilderness with multiple towns and dungeons. Because CthAngband is set in the Dreamlands, it features a whole new world of dungeons and dungeon guardians, the majority of which are Lovecraft-based.
The first version of Cthangband was Cthangband 2.1.0. which was released in 1998, and included only very minor changes to Zangband 2.1.0 - the existing variant upon which the code was based.
Cthangband 3.0.0 included a wilderness system with multiple towns and dungeons, and this broke save-game compatibility with previous versions.
The next major change was in Cthangband 4.0.0, which saw a large overhaul to the game mechanics; replacing the traditional class-and-level system with a skill system. While this version was popular with some players, the maintainer was unhappy with it and regretted its implementation; going so far as to pass maintainership onto someone else (David Thornley).
David Thornley quickly released Cthangband 4.1.0, but then never released another version and the game became defunct.
Nearly fifteen years after the release of Cthangband 4.1.0, Dean Anderson (the original maintainer) took back control of the game and released Cthangband 5.0.0 - a version that reverted many of the 4.0.0 changes and re-instated the class-and-level system.
Version 6.0 was the result of a complete re-write of the game in C#, which took over a year to complete, and consequently this version is Windows-only.
On August 14th 2018, Dean Anderson announced the 6.0 release of CthAngband on the Angband forums: announcement post
Since then, three minor updates have been released and the most recent version is 6.4, announced here: announcement post