Darfyx started off from my own need to memorize the gender of German nouns. I studied at Goethe Institut and my teacher suggested that we used paper cards to learn them.
For each card, I would write a noun on one side and its article on the other. Then I would shuffle them and start my sequence: read the noun, guess the article, check, and write down the ones I missed. Three to five times for each miss.
That simple system worked for me, I quickly memorized a lot of articles. But new nouns would turn up every class, and then the need to buy and prepare new cards. And some of them were easier; after only a few rounds it was a waste of time to keep them with the rest. But if I threw them out, I might forget them later.
The system's second version was a computer spreadsheet. It had a database that could be easily enlarged, with no need to buy or cut paper. The spreadsheet randomly picked a few nouns, I typed in their articles next to each one, and it graded them for me. The ones that I got right several times began to show up less and less often, just so I would not forget them. So my attention was always directed to the ones that were just added or harder to memorize.
I showed the spreadsheet to other students in my class and they liked it. Every class we would all write down the new nouns we had learned, and then at home we would add them to our spreadsheets. We began having several different databases, some of them with mistakes made by the students.
From this enhancement process resulted Darfyx. The database is centrally maintained to avoid errors. New words can be easily inserted, and the website automatically grades what the user answered.
We are currently not able to store one's individual history, but that will become available over the year. On the other hand, there are some other exercises and the interface is cleaner and friendlier than the spreadsheet or paper cards.
New releases are being announced in our facebook page. You can help, too, by sending us a note with your criticism or suggestions for improvement. Or simply keep practicing and telling your friends about it. After all, that is why I decided to make public this system that worked so well for myself. : )
Good luck in your studies,