Digidesign's DigiRack Mod Delay II is a free plug-in that comes with Pro Tools software. I've had it for a while, although I'm sure what the earliest version of Pro Tools is that comes with it. It installs automatically when you install Pro Tools, so you don't need to do anything further once you've got Pro Tools installed. The interface of the software looks like the other DigiRack plug-ins, as it simply has sliders to control each of the parameters. The parameters that it does have includes those for gain, mix, a low pass filter, delay, depth, rate, feedback, tempo, meter, and groove. Having the tempo and meter options is really cool, as it allows you to synch up the delay right with your other tracks. There really isn't anything complicated about the software, so a manual certainly isn't necessary.
I'm currently running the Digidesign DigiRack Mod Delay II plug-in 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 LE 8 with a Digi 002R audio interface or a Digidesign Micro Box if I'm working on my lap top away from home or a professional studio. I always run reverbs and delays on auxiliary channels to save processing power anyway, but this almost isn't necessary with this plug-in as it doesn't take up much processing power at all. In fact, this is the case with pretty much all of the DigiRack plugs-in, so I wouldn't worry too much about performance with this one.
Even though I've had it for years, Digidesign's DigiRack Mod Delay II isn't a plug-in that I find myself using very often. I get my delays and modulation effects with either outboard gear, pedals, or other plug-ins. However, I won't say that this is useless plug-in by any stretch, as I definitely think that users who have less options out there will find a lot of usage with the Mod Delay II. It isn't the best sounding plug-in in terms of sheer quality, but it will definitely get the job done and does offer up a good amount of varying tones. If you have Pro Tools in any form, you should already have this plug-in installed, so definitely give it a try!