CircleMUD is freely available, with restrictions provided by the CircleMUD license and the DikuMUD license.
CircleMUD is written completely in the C programming language. CircleMUD 3.1 has 40,538 lines, including comments and blank lines.
CircleMUD 2.0 has a memory footprint of about 2MB.
CircleMUD continued to grow by word of mouth until it had an average of 30 to 40 players online at any one time. Several times the MUD hit its maximum player limit of 58. However, due to a result of conflict that surfaced among the MUD's administrators, Elson permanently closed down CircleMUD on August 26, 1992. Several months later, in May 1993, Elson decided that the CircleMUD codebase could be used to fill a niche in the MUD community. He felt that there were many problems with the existing public MUD codebases such as portability and stability. He also felt that most developers wanted to start with a clean slate and did not want a codebase filled with fancy features.
Elson set out to achieve this goal in the summer of 1993. He began modifying the original CircleMUD codebase, and the first public release of CircleMUD arrived on July 16, 1993.
Since then CircleMUD has undergone many revisions. The last release by Jeremy Elson was 3.1., released on November 18, 2002.
In 2006, a number of discussions between Mark Garringer, Thomas Arp, Nathan Winters, and Jeremy Elson resulted in the release of CircleMUD 3.5 on December 11, 2006. Following this final release of CircleMUD, the name was changed to tbaMUD with the release of version 3.51, and this has now become the continuation of the CircleMUD line.
There have been a number of tbaMUD releases, with the latest being tbaMUD 3.57.