Social-IME
http://www.social-ime.com/

"Free IME software

This is a freeware IME composed by social method. It shares its dictionary and conversion feature on server via the Internet. Words and phrases inputted by users are saved to the dictionary on the server. It makes the dictionary and conversion feature more sophisticated.
Download is free.
(It's not clear that the software run on Windows except Japanese version.)

辞書をソーシャルに構築する
無料でダウンロードできる
インターネットに接続した環境で使用する
辞書・変換機能はサーバのものを使う
辞書が豊富で最新
予測変換が高度