Though this first alpha build of the OS X version of Trillian is still very preliminary and minimal - the functionality pulled through is about the same as the Flash-based web version - the code for every single feature on the Windows version is there in the underlying mediums. As the UI is expanded, those features will become available. The OS X version will be playing catch-up to the Windows one for a while yet, however.
The developer warns that the Mac OS X version is on a completely different release cycle than the Windows version, so non-simultaneous releases of Windows and Mac versions are likely.
The alpha build is available for users who have already set up Astra accounts and contact lists under the Windows version of Trillian.