Fontly

Features:

• Scales with resolutions above 1080p, so it works for 4k displays
• Lists all fonts from a directory tree in a list to quickly  browse through
• You can enter a custom preview text
• Can hide all fonts that don't contain all characters from the preview text
• Open the font in the  Windows Explorer to copy it to your project
• "Size is height" option to   compensate  font size differences

It probably works on mac/linux, too. I just don't have those systems available at the moment to test it. 

I am still adding features from time to time. Please comment below if you would like a specific function or have encountered a bug, thanks!