Glossolalia is a free, open-source language exercise app built with jsPsych by Bran[don] Papineau. No frills, no fees, no ads; just the most barebones language practice you can imagine. Each exercise simply drills the relevant forms or vocabulary.
While this won't get you fluent, I believe that language learning should be freely available to all, and if you find that this helps you learn some new words or nail some conjugations, that's all I want.
Click on a link below to get started. Numbers in parentheses = number of unique entries available in that exercise: