Dgraph

Instead of joining tables in SQL, you traverse relationships directly, which is orders of magnitude faster when queries go several levels deep. Go, Apache 2.0. Uses GraphQL as its native query language (plus its own DQL). Distributed by default. Shards data automatically across nodes. ACID transactions across the cluster, which most graph databases don't offer.

Fully open source, self-hosted. Dgraph Cloud existed as a managed service but the company has had a rocky history: funding issues, leadership changes, license controversies (they briefly switched to a restrictive license then reverted to Apache 2.0). The cloud offering's current status should be verified before relying on it.

Self-hosting requires at minimum 3 nodes for high availability (Dgraph Zero for cluster coordination + Dgraph Alpha for data). Expect significant ops burden. This is distributed systems work.

The catch: the corporate instability is the real risk. License changes, layoffs, and stalled development have shaken community trust. If you need a graph database with a stable company behind it, Neo4j is the safer bet (though it's source-available, not truly open source).