Want to delete app but can't force quit app through activity monitor
The instructions on their website say to logout using the FontYou icon in the top menu bar, and then drag the application to the Trash.

https://fontyou.zendesk.com/hc/en-us/articles/207787615-How-can-I-uninstall-Fontyou-

However choosing "Quit" from the menu will close the application and then let you delete it.