[0]https://news.ycombinator.com/item?id=17706776
[1]https://news.ycombinator.com/item?id=17846356
[2]https://news.ycombinator.com/item?id=13151790
[3]https://news.ycombinator.com/item?id=6461936
[4]https://news.ycombinator.com/item?id=14155074
[5]https://news.ycombinator.com/item?id=11408447
[6]https://news.ycombinator.com/item?id=17460513
etc.
TL;DR: You learn better if you revisit the material in exponentially-increasing time intervals. This can be automated.
SuperMemo is the original software (by the inventor of the technique). Anki is the recommended free alternative.
Can anyone recommend it for learning syntax?
I am going to give it a try
Edit: Googling on hackernews actually gives some previous discussions. One of those: https://news.ycombinator.com/item?id=10247471