The best replacement for fritz is chessmaster.

The best alternatives to fritz are rated as following:
★★★★★  chessmaster
★★★★  shredder
★★★★  rybka
★★  deep fritz
★★  houdini
★★  kramnik
★★  aquarium
★★  chessbase
★  kasparov
★  deep blue
★  billion
★  felix
★  nolan
  hiarcs
  june
  mary nolan
  deep junior
  devon
  laraque
  fritz
  igor
  arena
  shredder chess
  vladimir kramnik
  grandmaster

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

Other search terms related to fritz and their ratings are:
★★★★★ houdini
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