Ask HN: Is there an app to find similar fonts across platforms

Check this website out http://fount.artequalswork.com/ I don't know if that's what you are actually looking for.

Not sure if this is exactly what you need, but it has a list of the closest Google font to one you're looking for: http://joelcrawfordsmith.com/new/

I occasionally use What the Font to identify fonts... not always able to find all similar versions but it usually helps fill in the blanks on possible letter shapes of other letter in the font so I can hunt down similar fonts.

http://www.myfonts.com/WhatTheFont/