Cockos has released REAPER v1.54 for Windows and also made the first Mac OS X version available, albeit in "preview" form.

The Mac OS X version is a Universal Binary; it requires 10.4.x. It should be considered a "super-alpha-preview" as many things are not yet implemented, but you can at least load projects and edit, save, etc. You can load VST and JS fx, but can't access their UIs yet (you can automate them though).

Changes:

• Fixed recording MIDI items not updating track undo state.
• Better handling of audio drivers that give error boxes (no reopening).
• Mac preview version available on the forums [here].