My largest problem learning the language of the country I'm living in (Finland) is that the vocabulary doesn't want to stick. After a short time I've forgotten them again and honestly I'm not willing to sit down every evening after work to repeat them all. But hey, I'm sitting in front of a computer pretty much the whole day and I learned programming. Ergo:
This is a very basic tool that every few (pre-defined) minutes pops up a window and asks me one random word out of one (or more...