Digidesign's AIR Filter Gate is a unique plug-in that is available with Pro Tools 8. You can't get it anywhere else, but it does come free with the newest version of Pro Tools, and installs automatically when you install the host software of Pro Tools, so you don't need to do anything further to install it once you've got Pro Tools 8 up and running. It will show up under your modulation effects in your plug-ins. The interface of the plug-in is very basic, as there isn't anything fancy at all about the look of it. Digidesign (now strictly under the name Avid), has made these AIR (Advanced Instrument Research) plug-ins easy to use so that even those new to Pro Tools will be able to use them without a hitch. This one has sections for gate, filter, and modulation, each with their own parameters. There are also parameters to choose the pattern, which there are a ton of choose from, as well as for rate, swing, and mix. I don't think that they make any manuals for the AIR plug-ins as they should be easy enough to use without needing one.
I'm currently running the Digidesign AIR Filter Gate on a Mac Book Pro that has as 2.2 Ghz Intel Core 2 Duo processor and 4 GB of RAM. I just upgraded to Pro Tools 8 from 7.4 LE, which again is the only way that you can have the AIR Filter Gate plug-in. I run Pro Tools LE with a Digi 002R or a Micro Box depending on where I'm working from. Nothing about this plug-in will take up much of your processing power at all. If you've got an adequate system to run Pro Tools on already, you'll be fine with running this.
The AIR Filter Gate can produce some really interesting sounds. With a name like 'filter gate,' I expected it to be somewhere in between a traditional gate and a traditional filter, but it definitely isn't like that at all. It's hard to describe the bulk of the sound available here, but they are mostly in the range of choppy, pulsating modulation effects. I'd encourage you to check this one out if you've got Pro Tools 8, as there are a lot of cool creative things you can do with it, although I'm not sure there are any traditional uses for it.