As I mentioned in the previous paragraph, Anki and Duolingo are the closest competitors and actually installed on my phone; however the methodology of LAFWords is more relevant for me.
By the way, immersion-only approaches (reading books, watching shows) arguably the "purest" version of learning-through-context and also could be considered as an alternative. But immersion is slow and undirected; I learn whatever words happen to appear. This app front-loads the specific words I try to learn, which is a real efficiency gain over waiting, say, for exposure.
Thanks Konstantin — "actual bottleneck vs fake bottleneck" and "vibe-memorizing" are both getting borrowed from you as of right now. Three responses:
The before/after demo idea (flashcard pair next to ten contexts) is strong — you're right that reading the explanation is a much slower path than seeing the contrast in five seconds.
On immersion: agree with your read exactly. Immersion is the pure version but slow and undirected. LAFwords tries to compress the same mechanism onto the words you actually want to learn — the efficiency angle is the point.
More languages: yes, planned. Italian v1.1 (~6-8 weeks post-launch), German v1.2 (~3-4 months). More after those.