The best replacement for flex is flash.

The best alternatives to flex are rated as following:
★★★★★  flash
★★★★  silverlight
★★★★  ajax
★★★★  force
★★★  regular flex
★★★  note 3
★★  html5
★★  stiff flex
★★  explorer
★★  gwt
★★  one
★★  up
★★  uniflex
★★  stiff shaft
★  force fitbit
★  jawbone up
★  air
★  porter cable
★  rupes
★  core
★  fitbit one
★  lfr
★  up24
★  fitbit force
★  g2
★  rupees
★  regular
★  nike fuel
  extend
  hsa
  javafx
  muscle and fitness
  actionscript
  html 5
  jsf
  chevy traverse
  oxycise
  lex
  stiff
  samsung galaxy note 3
  metal duct
  accuflex
  lil flip
  nike fuel band
  traverse
  jawbone
  laszlo
  fitbit force review
  regular flex shaft
  nike fuelband
  orange whip review
  honda odyssey
  flash builder
  bowflex
  extjs
  stiff shafts
  ford edge
  bakflip
  uniflex callaway
  swing speed
  beadalon
  honda pilot
  chute

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

Other search terms related to flex and their ratings are:
★★★★★ java
★★★ .net
★★ mxml
★ spring
★ maven
★ blazeds
★ coldfusion
air
intellij
You have in mind a companion for flex and it is not yet here? Propose!



Google Trends

Scale is based on the average worldwide traffic of flex in all years. Click on graph for more.
flex
flash
silverlight