Cosign

#13 in Other

Andreessen Horowitz A16z · 2× · last seen Sep 26, 2026

31

Momentum

Cosign is a curated professional network for the startup community launched by a16z (Andreessen Horowitz) through its "New Media" product team. Rather than traditional self-reported profiles like LinkedIn, the platform organizes reputation through "Cosigns" – endorsements from people you've actually worked with – plus curated lists, an activity feed, and job postings from the startup industry. The product is currently in beta, available as a web platform at cosign.co, and free for users.

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