The best replacement for html5 is flash.

The best alternatives to html5 are rated as following:
★★★★★  flash
★★★  silverlight
★★★  xhtml
★★★  html4
★★★  native
★★★  javascript
★★  html
★  java
★  php
★  wordpress
★  flex
★  native apps
★  flash for games
★  html 5
  flash youtube
  wpf
  apps
  xhtml5
  flash performance
  css3
  jquery
  gif
  ios
  silverlight netflix
  native app
  xhtml 1.0 strict
  app
  css
  native ios
  flash games
  flash video
  xml
  ajax

Your alternative for html5 is not listed? Suggest!
Speaking about html5, one probably shouldn't forget about javascript.

Other search terms related to html5 and their ratings are:
★★★★★ javascript
★★★ css
★★ asp.net
★★ flash fallback
★★ css3
★★ coding
★★ browser
★★ ie8
★ jquery
★ dreamweaver cs5
★ jsp
★ svg
flash fallback player
struts2
asp.net webforms
You have in mind a companion for html5 and it is not yet here? Propose!



Google Trends

Scale is based on the average worldwide traffic of html5 in all years. Click on graph for more.
html5
flash
silverlight