From OSGeo Wiki
Geomajas is an extensible open source web mapping framework, enabling integrated GIS solutions for businesses and government.
It has an integrated client-server architecture, with a high focus on server-side integration of your data (be it through GeoTools or Hibernate).
This means that you apply your security and business logic on the server before anything is send to the client, resulting in robust applications (see architecture) and a real thin client.
Geomajas is an Open Source GIS framework. It's developed under the GNU Affero general public licence (AGPL) v3. Other licensing models for Geomajas are available through the copyright holder Geosparc.