The best replacement for synctoy is robocopy.

The best alternatives to synctoy are rated as following:
★★★★★  robocopy
★★★★  richcopy
★★★★  syncback
★★★★  freefilesync
★★★  offline files
★★★  briefcase
★★★  allway sync
★★  windows backup
★★  live mesh
★★  goodsync
★★  sync center
★  toucan
★  live sync
  cobian backup
  puresync
  second copy

Your alternative for synctoy is not listed? Suggest!
Speaking about synctoy, one probably shouldn't forget about task scheduler.

Other search terms related to synctoy and their ratings are:
★★★★★ task scheduler
You have in mind a companion for synctoy and it is not yet here? Propose!



Google Trends

Scale is based on the average worldwide traffic of synctoy in all years. Click on graph for more.
synctoy
robocopy
richcopy