This is awesome, it is all that I wanted from Google fonts but did not get. Definitely bookmarked. I can see this saving hours and hours of rummaging for fonts on Google and blog posts suggesting purportedly good font combinations.

Given this, here are a few things I would like that I find useful in google fonts

1. Info on how many weights are available (though the app gives the number of styles, it does not name them)

2. The ability to test with your own text. This is most useful when you are trying out fonts for headings. To be able to decide that in the app itself without having to iterate combinations by implementing in sites being developed will be a godsend.

3. This might be a bit too farfetched. The size of the font files for latin character sets. It can give you an idea of how much bloated your website is going to be. (This could be a filter maybe?) Typically now, I download each font file to inspect it's size.

Kudos!