I just did the NREMT under the MFR/EMR license (per our department)
I found JB learning test prep to be very helpful, as well as emt prep.
I didnt find any apps that helped.
JB learning was great as it was based on the book i had just completed. Also, its set up to be very similiar to the NREMT based test (in terms of computer multiple choice questions)
my favorite app has been pocket prep, i used it through out didactic, clinicals, internship and passed first attempt at 76 questions, it works best using nancy caroline/jb learning books as it references the pages of which the answers can be found on.