OpenWA
Free, Open Source, Self-Hosted WhatsApp API Gateway
...It exposes WhatsApp-related actions through HTTP APIs, making it easier to connect messaging features to custom apps, automations, dashboards, and business workflows. The project supports multiple sessions, so one instance can manage more than one WhatsApp account. It also includes a modern web dashboard for managing sessions, webhooks, and API keys visually. Its architecture is pluggable, allowing different database, storage, and cache backends depending on deployment needs. OpenWA is best suited for teams that want an open-source, configurable, and automation-ready WhatsApp integration layer.