Another significant release done at FOSS4G 2013 is the open source GeoServer 2.4. Along with MapServer, GeoServer is a popular server to disseminate geospatial data in WMS, and other standards of the same family.
Since I failed to find a nice list of what's new specifically for version 2.4, I feed you with a reminder of what GeoServer is according to their front page: "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. […] 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."