It's a free, open-source, frequently updated program with an active community.
If you don't see something you want in the program, you can ask the programmer to add it!
From the website:
Supports shared decks. You can subscribe to decks by your friends or teacher and new cards will enter your deck when you sync. To try it out, go to the Anki website, click "Manage" on the left, and then click "Share"
For example: I could share a Latin deck of 100 flashcards. You get a Key for my deck and subscribe to my deck. When I add cards to my deck, I sync it with the Anki server. The next time you open Anki and sync your deck with the server, you will automatically download the cards that I added to my deck. As many people as you want can sync up to your deck without your deck being changed by their progress.
I would love to see someone with a great flashcard deck share it through Anki! (I would share mine, but I have a lot of Lingua Latina Per Se Illustrata
cards that I don't believe would be right to share unless the other people owned the books.)http://ichi2.net/anki/