Are there any apps similar to Duolingo and Memrise for learning ASL?

Answer 1

There aren't any that are interactive like Duolingo is. This is because there would have to be a moving model for you to decipher phrases and sentences. There are video dictionaries like ASLPRO that model individual words but these don't give the Non-manual markers used or show the different kind of topic boundaries incorporated or the various kinds of sentences featured in ASL. The best way to learn is from interaction with members of the Deaf community (even if you are taking classes).

Answer 2

There are dictionary apps for looking up words, but none with full-fledged lessons on grammar and culture, as far as I know. The website I always recommend to people is Lifeprint.com, and the youtube channel of its teacher, Bill Vicars. His site includes full lessons for ASL 1-4, with word lists, sentences, and videos of his actual classes with students.