Google Input Tools/Methods:

• Input method (IME): https://www.google.com/intl/en/inputtools/services/features/input-method.html

• Try Google Input Tools online: https://www.google.com/intl/en/inputtools/try/

• Google 日本語入力 (JP IME): https://www.google.co.jp/ime/

  • CGI API デベロッパーガイド (Google CGI API for Japanese Input): https://www.google.co.jp/intl/ja/ime/cgiapi.html

Installable:

• Android: nowadays all are integrated into international Gboard app, https://play.google.com/store/apps/details?id=com.google.android.inputmethod.latin

• Chromium extesion: https://chromewebstore.google.com/detail/google-input-tools/mclkkofklkfljcocdinagocijmpgbhab