The runtime library which comes with the D compiler is called Phobos, named after one of the moons of Mars. Deimos (named after the other of Mars's moons) is the unofficial but commonly used name for a body of code which is provided by contributors to supplement the modules provided by Phobos.
Deimos utilises the namespace etc. For example, the bigint module may be imported by
the D statement:
import etc.bigint;. The etc namespace is described by the
official Digital Mars documentation as:
In addition to that description, the Digital Mars folk have stated that etc is also the appropriate place for contributor libraries which might one day migrate into Phobos. These are early days for D, and currently there is no official procedure for deciding what goes into etc and what doesn't. All I can really say is that I don't own this namespace, so if you write a library or module and would like it to go into etc, don't ask me if it's ok. Instead, get onto the D forum and the Digital Mars website and ask the guys there. I'm sure an official mechanism will arise in the near future.
The below, then, are contributions to Deimos currently available..