I have a backup of CVS; Jan Wieck is providing such for several
projects on developer.postgresql.org; he's generating a dump on a
nightly basis.

Based on that, I have built corresponding Mercurial, Darcs, and Git
repositories, those being reasonably widely available distributed SCM
tools.

I also generated a Subversion repo...

cvs2svn Statistics:
------------------
Total CVS Files:               570
Total CVS Revisions:          4370
Total Unique Tags:              30
Total Unique Branches:           2
CVS Repos Size in KB:        10069
Total SVN Commits:            1459
First Revision Date:    Fri Sep 22 19:14:09 2000
Last Revision Date:     Wed Sep 20 16:27:25 2006
------------------
Timings:
------------------
pass 1:     5 seconds
pass 2:     1 second
pass 3:     0 seconds
pass 4:     1 second
pass 5:     2 seconds
pass 6:     0 seconds
pass 7:     0 seconds
pass 8:   109 seconds
total:    119 seconds

A few little stats...

Repository         Size    Size of tarball
-------------------------------------------
Darcs              17660k        4916k
Mercurial          13656k        4412k
CVS                18096k        1928k
Subversion         19572k        5208k
Git                18444k        9092k

The Darcs and Mercurial repositories are directly usable as-is; you
don't need a further checkout to use them.

The others do.

All of these tools are pretty widely available, even on Windows and
MacOS.  There are LOTS of projects using CVS, many using SVN.

Git is obviously notable as the tool created to replace BitKeeper for
managing the Linux kernel.  Needs RCS, Perl, little else.

Mercurial was being proposed as alternative to Git.  Notable users
include Xen, ALSA, OpenSOLARIS.  Needs Python, and little else.
<http://www.selenic.com/mercurial/wiki/index.cgi/ProjectsUsingMercurial>

Darcs is a bit more "theoretical" in intent; there are a bunch of
projects using it...  <http://darcs.net/DarcsWiki/ProjectsUsingDarcs>
Neil Conway was using a Darcs repository to track PostgreSQL for a
while (notably during some of the Slony-II work).  Written in Haskell
(can be a chore to make available on obscure platforms); deployment of
repositories merely needs a web server.

Subversion: Requires Apache, Perl, Python...
-- 
(format nil "~S@~S" "cbbrowne" "ca.afilias.info")
<http://dba2.int.libertyrms.com/>
Christopher Browne
(416) 673-4124 (land)