Timeline

From the Conitec User Forum (Visit the thread here)

A brief history of GameStudio

1993 ACK-3D (Animation Construction Kit) by Larry Myers (Wolfenstein-like open source engine, downloadable at http://sunsite.lanet.lv/ftp/mirror/x2ftp/msdos/programming/ack/00index.html)
1994 ACK NEXT GENERATION by JCL (improved version of ACK 3D, open source)
1995 ACKNEX-2 written by oP group Germany for the German TV show X-BASE (Doom-like engine)
1995 ACKNEX-2 becomes Conitec property and is released as '3D GameStudio'
1997 ACKNEX-3 released (downloadable at http://server.conitec.net/down/a3.zip)
1999 A4 released (Windows based Quake-like engine)
2000 A5 released (Terrain engine)
2003 A6 released (Physics and Shaders)
2007 A7 released

A more in-depth history can be found in Tobias Runde's book Spielentwicklung mit 3D Game Studio

The first 4 historic AUM issues by Felicitas Oehler can be found here