FlipHack is a HackMaster hack for PalmOS that lets you rotate your screen 90, 180, and 270 degrees (and continue using your device).
There is some slowdown, but it is usable.
Released under GPL.
Source code is available from my web site.
Hoshi Takanori has released a DA to activate FlipHack from any application (using a DA launcher). It's called FlipDA
