I own both a PC and Mac. I bought Crossover for the Mac, which sets up a virtual Windows environment. Both Treesheets and Ecco run quite well in the system. So does Action Outline, although I don't use it too much.

With Ecco, I still haven't gotten it to run the Ecco extension just yet, but it works and I can copy/paste between both OS's.

For Treesheets, it serves as a good interim approach while Wouter works up a native Mac version.