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Kakugo vs Smouldering Durtles: catalog facts
Kakugo	Smouldering Durtles
Free Free and open source under GPL-3.0.	Free Free and open source under the Apache 2.0 licence; WaniKani itself is a separate service.
Android	Android
Covers hiragana, katakana and kanji Adapts review to the learner's pace	Native Android interface for WaniKani lessons and reviews Continues a well-known open-source client that was no longer maintained
Focused on memorisation, not grammar or speaking Android only	Only useful with a WaniKani account Android only
Downloadable app	Downloadable app
Open source	Open source
License: GPL-3.0	License: Apache-2.0
Not stated if an account is needed	Account needed
Not stated if it works offline	Not stated if it works offline
Official website Full listing and sources Checked October 2, 2026	Official website Full listing and sources Checked October 2, 2026

Catalog facts only. Anything “not stated” is unconfirmed. Check full listings for details.