A lot of free software uses a three point system: X.Y.Z where
- X is for compatibility breaking releases.
- Y is for other releases, with even numbers being stable and odd numbers being unstable.
- Z is for fixes.
This way version 0.28.1 is a stable release with one fix and 2.9.0 is an alpha release with zero fixes.
Some people also have fun developing their own schemes. E.g. Tex which by each release approxed Pi, with version numbers: 3, 3.1, 3.14, etc.
