[Corpora-List] Visual graph viewer/editor suitable for NLP applications?

[Roy Bar-Haim]

Dear all,

I'm looking for a visual graph viewer and editor, suitable for 
describing syntactic/semantic structures.

It should have the following features:
* Runs on Windows (a must)
* Supports any graphs, not only trees
* Supports multiple user-defined fields (features) for each node, and 
each edge
* Programmer-friendly format for input and output  files (preferably XML)
* Automatic layout
* Convenient editing of graphs

Preferably - free of charge for academic use...

I would be very grateful to get your recommendations on such a tool, and 
will post a summary of relevant responses I get.

Regards,
Roy Bar-Haim.