I like this: https://monkberry.js.org
riotux is inspired in Flux and Redux, but with more simple concepts. I think riotux has a smaller api and is very easy to understand.
I created glio.js, and yeah. I'm wrong about the text that was chosen in the modal popup. But, the 'Top-Direction' seems the user will leaves your site, tab... But the principal idea is trigger a callback when this happens.
Horrible UX? I think not. Exit popup is just one ideia about what you can make with glio.js. You can make much more, just depends you.