The best replacement for thinset is mastic.

The best alternatives to thinset are rated as following:
★★★★★  mastic
★★★★  mortar
★★★  adhesive
★★  grout
★★  tile adhesive
★  mastic backsplash
★  thick set
★  medium bed mortar
★  modified thinset
  non modified thinset
  mud set
  unmodified
  thickset
  mastic shower wall
  self leveling
  mastic ceramic tile
  dry set mortar
  unfortified
  joint compound
  mudset
  medium bed
  mud
  modified
  thinset
  mortar tile
  premix
  liquid nails
  unsanded thinset

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

Other search terms related to thinset and their ratings are:
★★★★★ hardibacker
★★★★ kerdi
★ ditra
You have in mind a companion for thinset and it is not yet here? Propose!



Google Trends

Scale is based on the average worldwide traffic of thinset in all years. Click on graph for more.
thinset
mastic
mortar