Peer Richelsen

Peer Richelsen is co-founder of Cal.com, the scheduling company that began as the open-source project Calendso. Its production code went closed source in April 2026. It is not his first company.

Growing Up on a Farm in Germany

He was born and raised on a small farm in Germany, he told Mercury; his father is a farmer and always working. His first business sold plastic sleeves for Magic: The Gathering cards after they went viral on Reddit. That interest became Mage Market, a marketplace for the cards that was accepted by Y Combinator in 2019 and shut down in 2020 during the pandemic.

Searching for an Open-Source Calendly

His next company, Leanhire, ran on Calendly, which was too limited for its needs, according to Product Hunt. After searching Google for an open-source alternative without success, he put up a waitlist and a Slack community. On Deck acquired Leanhire and he paused the idea, but people kept signing up. Bailey Pumfleet, one of the first sign-ups, reached out, and Richelsen funded the first year of development while Pumfleet joined as co-founder and CEO.