Alternatives to Network Analyst

If you are mostly interested in traversal/routing, go with pgRouting.

If you don't find what you need to do there, networkx has a freakishly large number of algorithms for graphs and now loads shapefiles out-of-the-box using OGR.

nx_spatial extends networkx in some minor ways mostly related to utility networks.

You might want to browse this post:

• Alternatives to pgRouting

and look through the previous posts using the Network and Routing tags

spatiaite has routing capabiliies with a GUI. I have never tried it. http://www.gaia-gis.it/spatialite/spatialite-network-2.3.1.html