While KaniManabu is an open source project and the source code is freely available, developing the app is not free. A lot of time, effort, and resources are put into developing the app to make an easier to use alternative to Anki made just for Japanese study.
Of course, since Apple requires an Apple Developer Program membership to distribute apps, I have no choice but to make KaniManabu a partially paid app. While all the features are available for free, there is a limitation on how many decks you can have. This number is 3, which should be enough for light users. The planned iOS version will be a paid release only with no limitations.
If you prefer separating cards out into separate decks or possibly use the planned miscellaneous deck feature, you can purchase a donation license to remove the limitation. See the main website for details. Active patrons can remove this limitation with their license, which unlocks access to all of our software. By purchasing a donation license, you can support continued development of our apps. A donation license can be used on an unlimited number of Macs you own.