You can find it in sandbox http://svn.boost.org/svn/boost/sandbox/msm/

Small precision, I use it as my "trunk" version. It is stable but the documentation still lags the code state (I am in the rewriting process). The last stable version and with up-to-date documentation (the one from the vault + a few bugfixes / performance improvements) is in: http://svn.boost.org/svn/boost/sandbox/msm/tags/version-2.0/

For SF right link is http://sourceforge.net/projects/boost-msm/

And I didn't even advertise it :) I plan to use SF so that one could request and try some features before they make it into the official code, but I need to finish the project page first, so for the moment, you will find not much there. Christophe