If you're looking for a stable version of D, you probably want to download the official releases. This page is for those who want to try out D on platforms that aren't yet officially supported, those who are adventurous and wish to try out the latest development (unstable!) version of D, and developers who wish to contribute to D development.
Getting the sources
The official release of DMD is available from the official download page.
This is for those who want to test or contribute to the development version of D. The latest source code for the D compiler, runtime library, and standard library are available on GitHub. To build a working D compiler toolchain, you will need to checkout at least dmd, druntime, and phobos.
Source code structure
The D source code assumes a particular directory structure, which you probably would want to adopt so that you don't have to fiddle with the Makefiles all the time.
For Posix, it is assumed that you will have a common root directory where the compiler and library sources will sit under. For example, you can choose the common root directory to be /usr/src/d, then you can checkout the sources under this directory:
mkdir /usr/src/d cd /usr/src/d git clone git://github.com/D-Programming-Language/dmd.git git clone git://github.com/D-Programming-Language/druntime.git git clone git://github.com/D-Programming-Language/phobos.git
Note: if you're planning to submit pull requests, you should replace the above URLs with the URLs for your fork of the official sources, not the official sources themselves.
You should end up with this directory structure:
/usr/src/d/ /usr/src/d/dmd /usr/src/d/druntime /usr/src/d/phobos
Building the sources
Assuming your sources are checked out in /usr/src/d, you can do the following to build them:
cd /usr/src/d/dmd/src make -f posix.mak cd ../../druntime make -f posix.mak cd ../phobos make -f posix.mak
Note that the compiler, runtime library, and standard library have to be built in that order, as each depends on the previous one.
If you're using a 64-bit platform, you may want to append "MODEL=64" to your make commands, as the default makefiles will build for 32-bit:
cd /usr/src/d/dmd/src make -f posix.mak MODEL=64 cd ../../druntime make -f posix.mak MODEL=64 cd ../phobos make -f posix.mak MODEL=64
After building, you should have a working D compiler in /usr/src/d/dmd/src/dmd. You may need to edit dmd.conf so that the compiler can find druntime and phobos. (TBD: expand on this)