The best replacement for fixed gear is single speed.

The best alternatives to fixed gear are rated as following:
★★★★★  single speed
★★★  freewheel
★★  road bike
★★  mountain bike
★  bmx
★  coaster brake
★  10 speed
★  single speed bike
★  single gear
★  track bikes
★  track bike
★  freewheel bicycle
  retractable
  in standard freewheel
  free wheel
  ten speed

Your alternative for fixed gear is not listed? Suggest!
Speaking about fixed gear, one probably shouldn't forget about chain tensioner.

Other search terms related to fixed gear and their ratings are:
★★★★★ chain tensioner
★★★★ clipless pedals
You have in mind a companion for fixed gear and it is not yet here? Propose!



Google Trends

Scale is based on the average worldwide traffic of fixed gear in all years. Click on graph for more.
fixed gear
single speed
freewheel