AceDB is distributed under the GNU General Public Licence except for a few parts which are distributed under the GNU Lesser General Public License. There is no fee, and no agreement to sign. You may redistribute AceDB unmodified without restriction, if you make changes to it, you are obliged to make those changes available in source-code form if you re-distribute them at all.

Please see http://www.gnu.org/copyleft/gpl.html and http://www.gnu.org/copyleft/lesser.html for the details.

We'd be interested to see copies of changes people make, with a view to incorporating them in the central AceDB source repository at acedb.org -- contact acedb@sanger.ac.uk for this.