PleXBMC is an addon with grafts Plex Media Server (PMS) access into XBMC. Also included are a number of modified skins with give easier access to media in a Plex-like environment.
Serviio is a free media server. It allows you to stream your media files (music, video or images) to renderer devices (e.g. a TV set, Bluray player, games console or mobile phone) on your connected home network.