Came across these two projects in the recent days:
Vital is the earlier effort, written in Java and no longer maintained. I mention it here because right now it is the most complete. Pivotal is a reimplementation in Haskell, compiled with GHC.
Both are document-based, graphical, interactive environments for programming Haskell based around functional reactive programming and direct manipulation. Basically a Self/Smalltalk-like interactive environment, for Haskell! Vital only implements a small subset of the language which is dynamically type checked; I'm not sure how far along Pivotal is, language-wise.
Pivotal is a project to watch. If it matures, then Haskell will be able to break free from the edit/compile/run cycle. (Which is a big if, sadly; projects in academia have a tendency to die off as soon as the guy finishes his thesis) And of course, we will finally see a statically typed language with a nice interactive development environment! (You can say all you want about the feature length of IDEA, Eclipse etc but they're not the type of development environment I have in mind when I say "development environment". They're more like fancy text editors).