As Anki is run as a business, it is difficult to accept donations. Instead, we make available AnkiMobile to raise funds for development. You can purchase AnkiMobile on your Apple mobile device, and the proceeds from it go towards supporting Anki's development.
For people who don't use Apple products, we hope to have more options available for supporting Anki in the future. In the mean time, please support Anki by telling your friends about it!