Apple's free IDE, Xcode, only provides support for C(++), Objective-C(++), Java, Applescript and Makefile. Although it's possible to use a Makefile for other languages, I think it's more practical to fully integrate them through dedicated plugins.
At the time I wrote this page, Xcode already has a working plugin interface (it's even used by CoreData compiler/editor, CVS/Subversion/Perforce integration, GDB debugging…). However this interface is not yet public, because not really finished. According to Apple, it'll be public in future release but no real date is provided: developers just have to wait :-(.
You'll find below some plugins made after reverse engineering Xcode's plugin API, and a documentation of this API for writing third party compiler or linker plugins.
|Fortran Plugin:||download - doc - source code|
|Ada Plugin:||download - doc - source code|
|OCaml Plugin:||download - doc - source code|
Plugins made by other people (ask me if yours is missing):
|Haskell Plugin:||web site|
|CSharp Plugin (C#/mono):||web site|
|Symbian OS Plugin:||web site|
|D Plugin:||web site|
|Another D Plugin:||web site|