FFFFALLBACK - A simple tool for bulletproof web typography.
ffffallback.com
From the page
Saved with the link. Notes from 2007 to 2016 are mostly the page's own words, so this is probably an excerpt.
Web fonts are here, sparking an exciting new era in web design. FFFFALLBACK makes it easy to find the perfect fallback fonts, so that your designs degrade gracefully.