Version numbering explained
Current version numbering
A revised numbering scheme is being used starting from version 1.9.7. See the libdeng2 article for details.
The Doomsday Engine was being developed as "unstable" software, which is why the "beta" label was used in the version numbers (e.g., Doomsday version 1.9.0-beta6.9). However, due to historical reasons, the label was not in the most logical place within the version number. For instance, if the version number was "1.9.0-beta6.8", one should actually think of it as "18.104.22.168-beta". Commonly the developers just used the end part, e.g., "beta6.8", when referring to a specific version within the 1.9 series.