acktung! is a map set for registered Wolfenstein. It was made by ack, and was initially released on September 27, 2003 in a 30-level version (Episodes 1, 2 & 3).
Some of these levels date back to the mid-1990's.
A version with all 6 episodes was released in December 2003. These 30 new levels were all newly made for the project. A full vanilla set (an increasingly rare kind), it's notable for receiving near-universal praise, often being cited as an example of worthwhile mapping.