I'm using Haskell to run a lot of instances of an Automated Thorem Prover, eprover. I have pasted a smaller version of my program at http://hpaste.org/54954. It runs eprover sequentially on all input files, with a timeout of 100ms. Unfortunately, it leaves a lot of zombie processes around, probably due to the fact that terminateProcess fails to terminate them, even though eprover terminates on SIGTERM.
They *do* terminate; a zombie is a dead process waiting for its parent to reap it with waitForProcess. There's also some POSIX stuff you can do to have them auto-reaped, but doing that correctly and portably is somewhat painful.