The best replacement for mythtv is xbmc.

The best alternatives to mythtv are rated as following:
★★★★★  xbmc
★★★★★  sagetv
★★★★  windows media center
★★★★  freevo
★★★  mediaportal
★★  mce
★★  media center
★★  plex
★★  wmc
★★  nextpvr
★★  tvheadend
★  eyetv
★  boxee
★  vdr
★  linux mce
★  beyondtv
★  gbpvr
  openelec
  media portal
  7mc
  beyond tv
  linuxmce
  mythbuntu
  windows mce
  vista media center
  windows 7 media center

Your alternative for mythtv is not listed? Suggest!
Speaking about mythtv, one probably shouldn't forget about hdhomerun.

Other search terms related to mythtv and their ratings are:
★★★★★ hdhomerun
★★★ hdhomerun prime
★★ lirc
★ cablecard
ceton
You have in mind a companion for mythtv and it is not yet here? Propose!



Google Trends

Scale is based on the average worldwide traffic of mythtv in all years. Click on graph for more.
mythtv
xbmc
sagetv