GIServer is a project based GeoTools. It is implementing functions as same as ArcGIS Server (10) REST interface, developers with ArcGIS Flex/JS/Silverlight API experience will have a free/open-source ArcGIS-liked server to use.
Open source project that offer summary and download services on this page is a project that carry out their development work on other open source development sites. Their work is linked to this page via a feature called OFI, and their work is not carried out here on OSDN site.