It is difficult to give something that is so young a five star rating, but this is already one of the best sites (along with stuff like Anki, Memrise, "X"Pod, Duolingo, LingQ, etc.) around for this and it is only getting better.
ReadLang saves you time by streamlining the process of creating a flashcard. Cards are created in the moment instead of having to stop what you are doing and open a new application to create a card or trying to remember at a later time.
I'd like to recommend a site you can use to read things online that allows you to translate words and phrases into your own language as you read. The site is called Readlang and I've already used it in a few classes which found the site really useful.
I love being able to upload videos from YouTube and sync the lyrics to them [...] And, the ability to instantly have words that I click on made into flash cards (that can be exported to Anki) is great, too. This site has so much to offer. :)
This is one of the most fantastic language learning tools I have ever encountered. I can progress quickly through a book I’ve never read, and more importantly, it’s enjoyable [...] and it serves as a great set of self-made index cards.
I use it everyday, I love how easy it is to pick new words I want to learn. I feel like I can finally read a book on a computer screen, something I've never been able to do before! So, thank you for this wonderful program :)