I have written a brief pdf document for whats new in v4.
chaldee1.gotadsl.co.uk/~richardb/upload/showthread.php?t=742
Catalyst v4 brings together a key number of features I have been working on for a while.
This version concentrates on ease of use.
Standalone operation.
Total backwards compatibility with v3 ( no new DMX channels ).
Show control features.
Pixelmad LED functionality. Multiple on-screen mixes.
Tiger ( OSX 10.4 ) compatibility. ( And 10.3 Panther ).
Runs on both.