neo4j/neo4j

Neo4j is a database that stores information as a graph — a web of nodes (things) and relationships (connections between things) — rather than as rows in static tables like a traditional relational database. The README calls it "the world's leading Graph Database" and says it offers "orders of magnitude performance benefits" for many applications compared to relational databases, while still providing enterprise-grade features like a query language and ACID transactions (guaranteeing that database operations are atomic, consistent, isolated, and durable).

How you get it:

• Neo4j Aura — a fully managed cloud version. You can sign up and start for free, no credit card required.
• Standalone server — download and run it yourself.
• Neo4j Desktop — a local developer tool for working with Neo4j databases on your own machine.

Running it locally: After building, you extract the package and run bin/neo4j-admin server start (or bin\neo4j-admin server start on Windows). It starts on localhost:7474.

Tools: Neo4j provides tools for querying, visualizing, and analyzing graph data. These work with both the managed AuraDB instances and self-managed databases.

Extending it: The project encourages experimentation. You can build extensions, develop libraries or drivers on top of it, or contribute directly to the core code. To have your patches accepted, you must sign a Contributor License Agreement.

Building from source:

• Requires Apache Maven 3.9.11 or newer, a recent Java VM, Bash, and Make.
• On macOS, install Maven via Homebrew (brew install maven). On Ubuntu, use sudo apt install maven openjdk-21-jdk and set JAVA_HOME to the Java 21 path.
• Build with mvn clean install -T1C (add -DskipTests to skip tests).
• Maven needs extra memory — set export MAVEN_OPTS="-Xmx2048m" if you hit build errors.
• On Linux-like systems, ensure your open-file limit is at least 40K (ulimit -n).

Licensing:

• Community Edition — open source, licensed under GPLv3.
• Enterprise Edition — includes additional closed-source components not in this repository and requires a commercial license from Neo4j.

Trademark: Neo4j's trademark policy is published on their website.

Note: The README does not describe the internal architecture, specific query language syntax, or performance benchmarks — those details are outside its scope.