Could you recommend me GraphDB that can be embedded in one app process like Neo4j, but must be free for commercial usage and must supports C# or Java?
Thank you for any advice!
Neo4j's open-source version doesn't limit the size of database.
Edit:
Neo4j's open-source version is licensed under AGPLv3, so you can't use it with closed source software products; your first unsupported instance of Neo Basic Server is free of charge though, so if you neither need commercial support nor the full feature set you are good to go for a closed source project as well.
But, good news for you: OrientDB is a java embeddable, fast, transactional (ACID), scalable, lightweight graph-document database, also supports SQL. And it's licensed under Apache 2.0, so OrientDB is free for any use.