FreeSurferDev is one of the InternalFreeSurferDistributions. It receives constant updates, which means it always has the newest features, as well as the newest bugs. It is at /space/lyon/1/fsdev/freesurfer_dev. We recommend that you do not use this distribution unless you have a good reason for doing so.
setenv FREESURFRER_HOME /space/lyon/1/fsdev/freesurfer_dev source $FREESURFER_HOME/FreeSurferEnv.csh
See also FreeSurferBeta and FreeSurferAlpha.