ZuluPad Pro 1.0 is availabe for $15. More info here. Click here to purchase it:

ZuluPad is the only cross-platform personal wiki. Currently it will run on Windows and OS X.

Current Free Release:

Download ZuluPad 0.42 for Windows

Download ZuluPad 0.3.8 for OS X (Universal Binary .zip file)

Download ZuluPad 0.42 for OS X (.tar.gz file)