The project provides development and test environments for lots of different hardware platforms, based on busybox and uClibc and configured to run under QEMU.
Most people want to do one of three things:
Download a prebuilt cross compiler and cross-compile stuff with it.
Go here and download the appropriate cross-compiler-$TARGET.tar.bz2 for your $TARGET, extract it, add its "bin" directory to your $PATH, and use the appropriate $TARGET-cc and $TARGET-ld and so on to compile your program. (The tool names have prefixes so they can be in the same $PATH as your host's existing compiler.)
Download a prebuilt system image, boot it up under the emulator, and compile stuff natively for a target.
Go here and download the appropriate system-image-$ARCH.tar.bz2 for your $TARGET, extract it, cd into it, and ./run-emulator.sh to boot it under qemu.
Alternately, you can run the script ./development-environment.sh, which is a wrapper around run-emulator.sh that feeds QEMU extra options to add memory (256 megs) and writeable disk space (a blank 2 gigabyte disk image mounted on /home) to provide a more capable development environment.
The system images contain native compiler toolchains, but if you install distccd on the host and add the appropriate cross compiler to your host's $PATH, the ./run-emulator.sh script will detect this and set up the system image to automatically use distcc to call out to the cross compiler through the virtual network, speeding up native builds significantly.
Build their own cross compilers and system images from source, using the build scripts.
Go to the downloads directory and grab the highest numbered release tarball, extract it, and run ./build.sh to list the available targets. The run ./build.sh $TARGET to compile the one you like. The results are in the "build> directory.
The build scripts are written in bash, and fairly extensively commented. All the scripts at the top level are designed to be run directly, and build.sh is just a wrapper script that calls them in order. The less commonly used scripts in sources/more are also designed to be run directly.
Go to the mercurial archive to grab the latest development version out of source control. If you don't want to use mercurial, you can grab a tarball of the current code at any time.
For the first two, the downloads/binaries directory has all the prebuilt binaries for the current release.
For the third, go to the downloads directory and grab a release tarball, or else look at the mercurial archive to grab the latest development version out of source control. (If you don't want to mess with mercurial, you can grab a tarball of the current code at any time.
If all else fails, look at the pretty screenshots.
A: You're using Ubuntu, aren't you? You need to install "qemu-kvm-extras" to get the non-x86 targets.
The Ubuntu developers have packaged qemu in an actively
misleading "interesting" way. They've confused the emulator QEMU
with the virtualizer KVM.
QEMU is an emulator that supports multiple hardware targets, translating the target code into host code a page at a time. KVM stands for Kernel Virtualization Module, a kernel module which allows newer x86 chips with support for the "VT" extension to run x86 code in a virtual container.
The KVM project started life as a fork of QEMU (replacing QEMU's CPU emulation with a kernel module providing VT virtualization support, but using QEMU's device emulation for I/O), but KVM only ever offered a small subset of the functionality of QEMU, and current versions of QEMU have merged KVM support into the base package. (QEMU 0.11.0 can automatically detect and use the KVM module as an accelerator, where appropriate.)
It's a bit like the X11 project providing a "drm" module (for 3D acceleration and such), which was integrated upstream into the Linux kernel. The Linux kernel was never part of the X11 project, and vice versa, and pretending the two projects were the same thing would be wrong.
That said, on Ubuntu the "qemu" package is an alias for "qemu-kvm", a package which only supports i386 and x86_64 (because that's all KVM supports when running on an x86 PC). In order to install the rest of qemu (support for emulating arm, mips, powerpc, sh4, and so on), you need to install the "qemu-kvm-extras" package (which despite the name has nothing whatsoever to do with KVM).
Support for non-x86 targets is part of the base package when you build QEMU from source. If you ignore Ubuntu's packaging insanity and build QEMU from source, you shouldn't have to worry about this strangely named artificial split.
The Linux filesystem is case sensitive, so the patch has to start with "uClibc-" with a capital C.