Timeline of the Linux Kernel releases. In gray are depicted the development branches and the small ticks from the the 2.6 branch are the minor releases. The minor that sticks out is the 2.6.16. The data was extracted from the timestamps of the files served by kernel.org. Tho dates, for 2.1.25 and 2.1.26 were wrong and were manually adjusted. The only omitted releases are the 2.2.0pre1 to 2.2.pre9.

Note that the proportion between the left (stable) and right (development) axes is 1 to 3.

Timeline of the FreeBSD releases. The data for this graph was collected from two sources: the /releases/ which provides month accuracy dates and also the modification time for the the x.x-RELEASE/README.TXT directories. The 2.2.9 release was announce on April 1st, 2006 with a funny message.

Update (2009/06/16): Thanks to Greg Troxel for indicating the proper major releases.

Timeline of the NetBSD releases. The NetBSD 3.1 and 3.0.2 were released simultaneously with the former containing several new features beside the critical bugfixes from the latter. The situation is similar for NetBSD 2.1 and 2.0.3 but they were released 3 days apart from each other (2.0.3 was the first).

Update (2009/06/16): Thanks again to Greg Troxel for indicating the proper major releases.

Timeline of the OpenBSD releases. The data was collected using the modification timestamps from the x.x/i386/MD5. As the FAQ indicates, the releases are 6 months apart. As Dr. Lamar says in Gattaca: Jerome, Jerome, the metronome.