The server is licensed under the BSD License.

Main (1.2.x) series:

• memcached-1.2.6.tar.gz -- July 29, 2008 [Changes]

Old (1.1.x) series, now maintenance releases only:

• memcached-1.1.13.tar.gz -- Sep 9, 2006 [Changes]

Subversion

• Subversion repository [svn log]

Git

Git stable tree [gitweb]

Dustin salling's tree (master binary protocol branch)

Toru Maesaka's tree (master storage engine branch)

Quick git tutorial: git clone http://consoleninja.net/code/memcached/memcached.git
'master' is tracking stable upstream.
create a branch:
git checkout -b newbranch
work work work
git commit -a
update the tree:
git pull

Working with a branch tree:
git clone git://github.com/dustin/memcached.git
git branch -r (show remote branches)
git checkout --track -b lbinary dustin/binary
etc.
Intro to git for SVN users
Git documentation

The client APIs, licensed individually, are available for download on the Client APIs page.