Now, to be fair, Cerulean Studios states that this is in fact not a port at all, but a ground-up reimplementation of Trillian. The teaser screenshot on their announcement page is certainly intriguing. From the announcement:
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.
Currently it appears that test versions are only being offered to testers of the current Windows-based Trillian Astra. Click through to the announcement page if you'd like to sign up to test Trillian on your Mac.