The best replacement for readability is legibility.

The best alternatives to readability are rated as following:
★★★★★  legibility
★★★★  pocket
★★★  instapaper
★★  legibility typography
★★  leveling
★  instapaper ipad
★  safari reader
★  writability
★  safari reading list

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

Other search terms related to readability and their ratings are:
★★★★★ instapaper
★ safari reading list
You have in mind a companion for readability and it is not yet here? Propose!



Google Trends

Scale is based on the average worldwide traffic of readability in all years. Click on graph for more.
readability
legibility
pocket