XTDB is an open-source document database with bitemporal graph queries. It natively supports two time axes for each record: valid time, when a fact occurs, and transaction time, when a fact is processed and recorded by the database. Support for bitemporality is beneficial in numerous scenarios, including analytical use cases executing time-aware queries; auditing historical changes to facts; supporting distributed data architectures that must guarantee globally consistent point-in-time queries such as data mesh; and preserving data immutability. XTDB takes information in document form, expressed in the Extensible Data Notation (EDN) format, a subset of the Clojure language. XTDB supports graph as well as SQL queries and is extensible through a REST API layer and Kafka Connect, among other modules. We're excited to see a growth in adoption of XTDB and the addition of features such as support for transactions and SQL.
Crux is an open-source document database with bitemporal graph queries. Most database systems are temporal, meaning they help us model facts along with the time at which they occurred. Bitemporal database systems let you model not just the valid time the fact occurred but also the transaction time when it was received. If you need a document store with graph capabilities for querying the content, then give Crux a try. It's currently in alpha and lacks SQL support, but you can use a Datalog query interface for reading and traversing relationships.