ECL partially moved to the common-lisp.net server. If you keep up to date with the latest improvements and fixes of the ECL environment, you can use CVS to pull the latest sources from there.
If you have a modern version of the CVS program, such as the one shipped with Mingw or with any Linux distribution, the command to get the development sources is
# ADDRESSemail@example.com:/project/ecl/cvsroot # cvs -z3 -d :pserver:anonymous:$ADDRESS co ecl
Additionally you can test ECL with Paul Dietz's ANSI test suite. For that you need to download some additional files using
# cvs -z3 -d :pserver:anonymous:$ADDRESS co ecl-test
Typing make from the top of the ecl-test directory will download the latest version of the test suite and run it using the version of ECL which is available on your machine.
Additionally you can browse the ECL source code and download tarballs using this address.
By user request we also host three GIT mirrors of the full CVS history of ECL. They are updated every 15 minutes, just like the anonymous CVS server mentioned before. They can be cloned as follows: