The best replacement for webgl is canvas.

The best alternatives to webgl are rated as following:
★★★★★  canvas
★★★★★  opengl
★★★★  svg
★★★★  three.js
★★★★  canvas 2d
★★  x3d
★★  native client
★  stage3d
★  opengl es 2.0
★  css3
  unity3d
  nacl

Your alternative for webgl is not listed? Suggest!
Speaking about webgl, one probably shouldn't forget about three.js.

Other search terms related to webgl and their ratings are:
★★★★★ three.js
★★★ canvas
You have in mind a companion for webgl and it is not yet here? Propose!



Google Trends

Scale is based on the average worldwide traffic of webgl in all years. Click on graph for more.
webgl
canvas
opengl