Hook0 is an open-source webhooks service for developers. One API call hands off event delivery, and the platform takes care of routing, retries, security and monitoring.

One-call sending - a single API call fans an event out to subscribers.
Retries - failed deliveries are retried automatically.
Security - signed payloads with HMAC signatures.
EU hosting - runs in France with GDPR-oriented handling.
Open source - the full server source is published under SSPL-1.0.

It suits SaaS teams that need customer-facing webhooks without building delivery infrastructure. A free plan is available with no credit card required.