This stuff is in English although my native language is German. This is an explanation why. It goes along the roads of ELFE but concentrates on my personal view. It would be obviously pointless to write this in English as well, so I'm switching to German here.
Vocaber is an online tool for the rapid acquistion of new vocabulary. Vocaber grew out of a need for a simple way to learn words without having to worry about forgetting them along the way. Vocaber acheives this using a spaced repetition algorithm which automatically retests you on words at the appropriate frequency to move them from short-term memory into long-term memory.
N. Fuchs. Proceedings of the 13th International Conference on Conceptual Structures (ICCS 2005), volume 3596 of Lecture Notes in Computer Science, page 51-51. Springer, (2005)