Neo4j comes as standalone server. Easy to download and start. It has an accessible Web-UI and a comprehensive REST-API. Neo4j-Server is also available at Heroku and for cloud setup. The drivers for non-JVM languages all work with the Neo4j-Server
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Neo4j Server Web Interface
The Data Browser Tab offers a handy visualization of your graph. You can select the nodes to be shown by id, index lookup or cypher query. A style editor will adapt the visualization to your needs.
The Neo4j Server Web Interface was written using arbor.js and canvas.