I think Mnemosyne already supports having more than two sister cards under the hood, and might be able to import N‐sided imports from Anki files, but there is still no way to use the Mnemosyne UI to create a vocabulary entry with three sister cards (Foreign Word→Translation+Pronunciation, Translation→Foreign Word+Pronunciation, Pronunciation→Foreign Word+Translation). Such a feature would be very useful for learning vocabulary in foreign languages with different writing systems. Additionally, implementation could be rather simple, such as through an additional checkbox for 'Also Test Listening Comprehension' when creating or editing an existing card.