Evolution API is the default answer in most self-hosted WhatsApp tutorials, and deservedly so. It is genuinely open-source (Apache 2.0), actively maintained by the Evolution Foundation, and unusually well connected — native integrations for n8n, Chatwoot, Typebot, Dify and OpenAI, event streaming to RabbitMQ, Kafka, SQS, NATS and Pusher, and media to S3 or MinIO. If you want to own the whole stack and wire it into your own infrastructure, it is an excellent choice and this page will not pretend otherwise.
What it does not do is take care of you. Its own requirements are Node.js 20+, PostgreSQL or MySQL, and Redis for caching. That is three services to run, back up, secure and upgrade before you have sent a message. There is no anti-ban pacing layer — no warm-up schedule, no per-number rate ceiling, no risk score, no quiet hours — so if you point a workflow at it and it sends faster than a person would, nothing in the system will stop you. There is no interface either: no inbox, no message archive you can search, no scheduling queue, no way for a non-developer on your team to see what happened.
SocialMate is not the open-source option, and that is the honest trade. It is a maintained commercial product on a flat license. What you get for it is the layer Evolution deliberately leaves to you: a 6-phase warm-up, per-number minute/hour/day caps, live risk scoring with automatic cooling, human-like typing and jitter, night-mode quiet hours, and per-account device-fingerprint isolation — plus a GUI, a local message archive with full-text search, a smart queue with scheduling and retry, and someone to email when it breaks. It deploys the same ways Evolution does, and one more: your own desktop, with no server at all.