Serviio is a free DLNA media server. It allows you to stream your media files (music, video or images) to any DLNA-certified renderer device (e.g., a TV set, Blu-ray player, games console) on your home network.
Serviio is based on Java technology and therefore runs on most platforms, including Windows, Mac, and Linux (incl. embedded systems, e.g., NAS).
While Serviio is free, additional features are available in the Pro version.