GML format

GML (Graph Modelling Language) is a "hierarchical ASCII-based file format for describing graphs" Wikipedia. It supports attaching arbitrary information to graphs, nodes and edges, and is therefore able to emulate almost every other format.

More information at the official GML homepage (last modified on July 20, 1997).

An example
Here is how a simple example of a circle of three nodes.

graph [ comment "This is a sample graph" directed 1 id 42 label "Hello, I am a graph" node [ id 1 label "Node 1" thisIsASampleAttribute 42 ]   node [ id 2 label "node 2" thisIsASampleAttribute 43 ]   node [ id 3 label "node 3" thisIsASampleAttribute 44 ]   edge [ source 1 target 2 label "Edge from node 1 to node 2" ]   edge [ source 2 target 3 label "Edge from node 2 to node 3" ]   edge [ source 3 target 1 label "Edge from node 3 to node 1" ] ]

Converters
TODO: add ways to convert from GML and into GML.