Since we get asked a lot, here's the tools we use for software development:
[Minimalist GNU for Windows], a port of GCC and accompanying utilities to Windows. Includes the debugger, gdb.
[Qt] is both a widget toolkit and a set of very handy utility templates like container classes, network handling. It's all crossplatform, meaning that Murmur runs on pretty much any modern architecture, including the qmake files. I have a few projects that doesn't use Qt at all, but uses Qmake :)
[Textpad], a lightweight editor for Windows. Not the best or most flashy, but works for me.
[Joe's Own Editor] is my preference for UNIX editor. It's definitly not the most userfriendly, most powerfull, most fancy or least buggy editor, but I sort of got stuck on it.
Speaking of editors, if anyone has a suggestion for a good editor that forcibly auto-indents, supports code collapse (so just the prototype is shown), highlighting, code completion and compiler output parsing, then send me an email.
"[Valgrind] is an award-winning suite of tools for debugging and profiling Linux programs." We use this to make sure the server has no memory leaks.
[CodeAnalyst for Windows] is AMD's performance analysis software. I like Intel VTune better, but VTune runs exclusively on Intel processors, and I have a Athlon-64. A proper run with the profiler will give you what module Mumble spends time in (should be 90% or so in libspeex.dll), and if it had understood the MinGW debug format we would get the time distribution per function as well.
[MSDN] is Microsoft's developer website, and contains an updated decription for each and every function available on windows. I find the website easier to use than the MSDN helpfiles, as the website has all the files searchable as one, instead of having one file for the DirectX SDK, one for the Platform and so on.
[SourceForge] is not only a website, it's a very handy tool. It comes with CVS, which we use extensively, as well as forums, wikis and mailing lists.
[Nullsoft Scriptable Install System] is the installer made famous by WinAmp. It's a easy-to-use, efficient and userfriendly install system; it took us less than 15 minutes to make the first installer for Mumble.