Source Code
The CouchDB code can be found in the Apache Subversion repository. The repository can browsed online here.
You can check out the code using the svn commandline client as follows:
svn co http://svn.apache.org/repos/asf/incubator/couchdb/trunk couchdb
Committers should use the HTTPS URL:
svn co https://svn.apache.org/repos/asf/incubator/couchdb/trunk couchdb
More information on the Subversion repository at Apache is available here.