Knock

Knock is a New York-based notification and customer-engagement infrastructure company that gives developers a single API and dashboard to design, manage, and deliver messages across in-app, email, SMS, push, and chat channels. Founded in 2021 by former Frame.io leaders Sam Seely and Chris Bell, Knock lets product and engineering teams ship cross-channel notification workflows without building and maintaining an in-house system, and now powers messaging for companies like Vercel, Webflow, Amplitude, and Clay.