There are also Shapeshift : https://github.com/McPants/jquery.shapeshift
and Gridly : http://ksylvest.github.io/jquery-gridly/
which are good alternatives to Gridster. (yet note that Gridly is for squared tiles only)
Edit :
Packery is also very interesting : http://packery.metafizzy.co/
. However it requires a commercial licence for commercial project otherwise :
For non-commercial, personal, or open source projects and
applications, you may use Packery under the terms of the GPL v3
License.
Edit 2 : This one may also be useful : https://github.com/uberVU/grid