Twisted fails scads of tests on Windows. You can see that here: http://twistedmatrix.com/buildbot/ I know that there are at least a few people on this list that use Twisted on Windows. Doesn't it bother you that it's broken? If you're a windows developer, help out and fix some tests! A few Twisted hackers, Justin J. in particular, are hard at work to make it scale and perform well on Windows, but in addition to the rocket-science of IOCP there is quite a bit of grunt work to do, especially in the area of understanding why certain tests fail when they pass on other (more UNIX-y) platforms. So please, try debugging some Twisted unit tests and either submitting bug reports explaining what's going on so an existing Twisted dev can fix them, or submitting patches that we can apply. The real bonus for you if you're using Twisted on Windows in some commercial capacity is that once the buildbot turns green, test fascists like JP (or, on off days, myself) can revert changes which break it, and enforce a higher standard of quality for portability of Twisted code. Right now it's hard to convince developers to not make it fail _more_ tests, since hey, it's broken already, right?