I'm currently running the RTAS version for Mac of the Blue Cat Audio Blue Cat's Chorus plug-in, as right now I've got a bunch of free Blue Cat Audio plug-ins on my system at home. This system consists of Pro Tools LE 8 and a Mac Book Pro with a 2.2 Ghz Intel Core 2 Duo processor and 4 GB of RAM. I run Pro Tools LE 8 with a Digi 002R audio interface. Blue Cat's Chorus plug-in won't take up much of your processing power at all, so I can't foresee too many users having performance problems with it.
It's tough to find free plug-ins that are available in all plug-in formats and for both Mac and PC operating systems, but that's exactly what you'll get with the Blue Cat Audio Blue Cat's Chorus as well as their other plug-ins. Of course the plug-in doesn't have the most realistic chorus tone I've heard, but it's still usable for sure, and considering the plug-in is free I can't really do any complaining. I've only been using this plug-in for a relatively short amount of time, but I'm finding myself using it more and more when I need some simple chorus. At the price of free, there's no reason not to try it for yourself!