Media Browser is a great alternative to Windows Media Center for consuming media content on a Windows PC. Unlike Media Center there is active development on Media Browser and today they have announced Media Browser 3. The system has a central server design where you can centrally manage plugins and all you content and then there is a Media Browser Theater client for Windows as well as client apps for Android, windows 8/RT and Windows Phone. Media Browser 3 looks fantastic and is a great challenger to XBMC and is probably what Media Center could have been had development been continued.
This video gives you a good idea of what to expect. Look out for the beta in March with general release targeted for April.