We need simple readers for

• SIF (cytoscape) (I've got some code already TC)
• Pajek
• GML https://github.com/kgn/pygml
• NNF
• SBML (qual) (I've got some code already)
• PSI-MI
• Biopax

conversions between formats is not always possible though.

reference: http://wiki.cytoscape.org/Cytoscape_User_Manual/Network_Formats

See also igraph, networkx packages and Gephi (https://gephi.org/users/supported-graph-formats/)

http://sbfc.sourceforge.net/mediawiki/index.php/Main_Page#Conversion_using_a_console

https://www.ebi.ac.uk/biomodels/tools/converters/results?emailAddress=