From OpenNMS

Stable, development, and release candidate numbering

For a three part version number in the form M.N.O:

Even middle digit N 

Stable; 1.6.8 is the latest stable release.

Odd middle digit N with the final digit O < 90 

Development; 1.7.8 is the latest development release.

Odd middle digit N with the final digit O >= 90 

Release candidate (AKA: beta release) for the next stable release M.(N+1).0; 1.7.90 will be the first release candidate for 1.8.0.

What happened to 1.4?

We decided that the changes between 1.2.x and later 1.3.x releases were so huge that a single minor version bump was insufficient for the next stable release, so we went straight to 1.6 for the stable release. According to the scheme above, the release candidates for the 1.6.0 stable release started at 1.5.90.

Quick Reference

Existing Releases

1.2.9 

Old stable release. The last of the 1.2.x releases. No longer supported.

1.3.11 and 1.5.97 

Last unstable releases leading up to 1.6.0. No longer supported.

1.6.8 

Last stable release of the 1.6.0 series

1.8.12

The latest stable release

1.9.8 

Latest development release. Not suitable for production use in most environments, but contains the newest features.

Future Releases

1.10.0 

Will be the new stable release, superseding the 1.8 stable releases.

1.11.0 

Will be the new unstable release when 1.10.0 is released.

Code availability

100% of our code is "generally available" from SourceForge's servers. Stable branches focus on bug fixes, unstable branches on new features and architectural improvements. See Developing with Git for details on accessing the git repository and Branch Management for branch policy.