Sonalksis' MultiLimit plug-in is one of four that comes in the Sonalksis Mastering Suite. Both the plug-in and the bundle are available for both Mac and PC operating systems and in RTAS, VST, or Audio Unit plug-in formats. The interface of the plug-in itself is fairly easy to understand if you understand the principles of a limiter. It is split up into five separate frequency bands, which each allowing you to control parameters for drive, gain, release, solo, and on, and a series for four sliders above them to allow you to set each cross over frequency between each of the bands. There are then more general parameters for threshold, ceiling, release, smooth, and clip. Once you break it down it should be pretty easy to understand, and there's a nice graph there that shows you where your bands are on the frequency spectrum. A manual shouldn't be necessary, but while I'm sure there is one for it, I haven't seen it.
I've used the Sonalksis MultiLimit plug-in at a studio I was recently working out of, but I don't have it on my system at home. I was running it on a Pro Tools HD system, so we didn't have any issues with it or printing with it as we were doing. It probably does take up a decent amount of processing power, but it still shouldn't give you much of a problem if you're currently comfortable running RTAS or other native plug-ins.
Sonalksis' MultiLimit plug-in from their Mastering Suite is a great sounding multi-band limiter for your DAW. It's easy to use and still gives you a lot of control over your sound, as between the five bands you should be able to get as specific as you'd like. In general the sound is pretty punchy, and you can get your mixes a good bit louder with this. It's probably not worth buying it unless you're going to just go for the full Mastering Suite bundle, as not only are the others great to have to do a complete mastering job, but it's also cheaper to get everything together. Check this out if you're looking for some good mastering plug-ins!