Canna is a Japanese input system available in Free Software.
Canna provides a unified user interface for inputing Japanese.

Canna supports Emacs, kinput2 and others. All of these tools can be used
by a single customization file, romaji-to-kana conversion rules and
conversion dictionaries, and input Japanese in the same way.

Canna converts kana to kanji based on a client-server model and supports
automatic kana-to-kanji conversion.