Digidesign's AIR Lo-Fi is a plug-in that comes free with the purchase or upgrade to Pro Tools 8. I recently made the jump on my home system to Pro Tools 8, and I'm glad a did as you get a whole bunch of new plug-in with Pro Tools 8. You don't need to install AIR Lo-Fi at all once you've installed Pro Tools 8, as it is taken care of in the initial process of installing Pro Tools 8 without having to do anything extra. The interface of the software is actually a bit complex for a lo-fi plug-in! Most lo-fi plug-ins only have a few parameters, so it is cool to see one with a whole onslaught of parameters to work with. This one has sections for anti-alias, which has parameters for pre and post, for LFO, envelope modulation, and distortion. The LFO has knobs for rate, wave, and depth, the envelope mod has those for attack, release, and depth, and the distortion section has parameters for clip, noise, and rectify. Lastly, it has main parameters for sample rate, bit depth, and mix. Being able to change the sample rate and bit depth on the fly like this are perhaps the coolest features that AIR Lo-Fi has to offer. I don't believe that they even make a manual for this plug-in, but you wouldn't need one either way.
I'm currently running the Digidesign AIR Lo-Fi plug-in and Pro Tools 8 on a Mac Book Pro that has a 2.2 Ghz Intel Core 2 Duo processor and 4 GB of RAM. I run Pro Tools 8 with a Digi 002R audio interface. I just upgraded to Pro Tools 8 from 7.4 on my home system, but had been using at a professional studio since it came out. However, I didn't use the Lo-Fi plug-in at all until getting it at home. Thus far, I can't say I've had any problems running the plug-in within my home configuration. I should say that I've only had a need so far to run one instance of the plug-in at a time, and I really don't see that changing. I would imagine that most users won't be using too many of these at once, so the majority of users will be fine regardless of their system specifications.
While not always needed, the Digidesign AIR Lo-Fi can definitely do some cool things to your sound. It goes behind just being your average "lo-fi" plug-in, as it gives you access to control that you don't normally get with plug-ins of this nature. Pair this up with the fact that it is a free bee with Pro Tools 8, and you've got yourself a great deal here. Even if it isn't the type of plug-in that I'll be using very often, I'm very happy to have it around for when I might need it, especially considering that I probably wouldn't ever have the chance to spend money on a plug-in like this...