Raft is a personal assistant you talk to in direct messages (iMessage, Slack and the like). If you ask it to, it can read your Gmail and see and change the events on your Google Calendar, so it can answer questions about your mail and keep your schedule.
You connect your Google account only by opening a link Raft sends you, and you can disconnect it at any time. See the privacy policy for what Raft does with your data, and the terms of service.