Quite a while ago we decided to give free JRebel licenses to valuable F(L)OSS projects.
GeoServer is one of them:
GeoServer is an open source software server written in Java that allows users to share and edit geospatial data. Designed for interoperability, it publishes data from any major spatial data source using open standards.
Being a community-driven project, GeoServer is developed, tested, and supported by a diverse group of individuals and organizations from around the world.
GeoServer is the reference implementation of the Open Geospatial Consortium (OGC) Web Feature Service (WFS) and Web Coverage Service (WCS) standards, as well as a high performance certified compliant Web Map Service (WMS). GeoServer forms a core component of the Geospatial Web.