Verb Conjugation Practice 動詞の活用
This is like me trying to do potential, causative, causative-passive, and passive forms. I find myself doing the conjugation step by step which is way too slow for speaking.
This is by far the best interface that I’ve used! It doesn’t have causative-passive, though. That’s okay because I can practice that when I get the others down.
Alternatives
For my reference.
This one has more challenging modes, like changing from a non-dictionary form.
Don’s Japanese Conjugation Drill
For causative-passive practice
Workbook: Verb Conjugation (Causative-passive) – Lesson 23 | Genki Study Resources – 2nd Edition
And the above is also a great resource if you’re using the Genki textbooks.