Very nice.

This clearly takes a lot of inspiration from LingQ, but fixes some of LingQ's more glaring challenges such as letting you use a real dictionary, instead of relying on definitions that were crowdsourced from other learners using the app. (And therefore full of quality problems an inaccuracies.) On the other hand, it sounds like some nice features aren't implemented yet, or maybe not even planned, so maybe LingQ is still a good option if you don't want to hassle with self-hosting a webapp or hunting down your own resources, and don't mind paying the subscription fee.

All in all, though, it looks very promising!