iDrum is now out for Windows. For what it does, which is quick beat sketching, it's a solid product with good VFM.
The GUI is friendly and easy to work with. Beats can be "drawn" in with easy velocity shading. A selector at the top of the interface lets you pick from one 16th pattern bar, 2 32nd bars, and three 64th bars - be aware these bars are layered, which is not obvious out of the gate.
There are plenty of sounds available in the demo, and once the free content is downloaded (from your iZotope account after purchase), the number of sounds available increases dramatically. I have yet to hear a clunker in any kit so far.
The number of features available are too numerous to list here, and good, but there are noticeable gaps. While a pattern can be exported to MIDI via simple drag and drop, pattern import is impossible. Forget your MIDI grooves - they ain't happenin here. :(
Documentation is clearly geared towards the original Mac version, and although a node has been given to the new Windows release, there are errors, such as the location to place alternative skins (and I still haven't found the proper location for them). The builtin help file also shows Mac menus, not Windows, and some Mac menu options aren't present in the Windows menu version.
Presets are really there to illustrate the various kits. While they are good, there are not a lot of them.
Customer support is limited to the help file mentioned previously and an online FAQ at iZotope's site, plus email support. I have had no crashes in the standalone or VST, but I'm lumping this in with documentation in my rating. Given the price point, I can't complain more than I already have.
If you want to sketch out a drum part manually in a lightweight app, iDrum will do the job just fine.