The Doom source code was released on December 23, 1997, initially under a not-for-profit license. Later, permission was granted to re-release the source code under the GNU GPL on October 3, 1999. Before release, the source code was tidied up by Bernd Kreimeier; the source release includes a changelog of his contributions. Several documentation files are also included. The original plan for the source code release involved a book Kreimeier was to write on the Doom engine; however, due to Doom's decreasing relevance in the gaming community, it was eventually judged not to be a marketable idea, and the project was abandoned. The source code was then released to the public.