OpenBSD's OpenSSH portable version

Normal OpenSSH development produces a very small, secure, and easy to maintain
version for the OpenBSD project. The OpenSSH Portability Team takes that pure
version and adds portability code so that OpenSSH can run on many other
operating systems (Unfortunately, in particular since OpenSSH does
authentication, it runs into a *lot* of differences between Unix operating
systems). 

The portable OpenSSH follows development of the official version, but releases
are not synchronized. Portable releases are marked with a 'p' (e.g. 3.1p1).
The official OpenBSD source will never use the 'p' suffix, but will instead
increment the version number when they hit 'stable spots' in their development. 

WWW: http://www.openssh.com/portable.html