There are native webinar integrations with Zoom, WebEx, and GoToMeeting. Act-On does not currently have a native integration with Hopin.
Zapier will allow you to integrate the two platforms without a native integration for some workflows. This is based off of Actions and Triggers. We are limited to the Actions and Triggers Zapier has built for communication between Hopin & Act-On.
Hopin: Get Event Registrations
Act-On: New Form Submission
Act-On: New Automated Program External Call
Hopin: Get Redeem (Token of some kind, I think this has to do with a unique conference/meeting access item)
Act-On: Add Contact to List
Act-On: Create Form Submission
Act-On: Update or Create Contact
You will need a Zapier account to build this out.