I wanted to flag up our free ArcToolbox tool to this community (hope that's appropriate, please remove the post if not!).
sDNA fills a slightly different niche to ESRI network analyst - I use both tools myself and both are good for different tasks. While ESRI use origin/destination points as a basis for analysis, we use links themselves as the fundamental unit. This is useful in the absence of OD data - especially combined with angular analysis which can proxy missing impedance data such as pedestrian route preference or vehicle travel time.
sDNA computes a variety of closeness, betweenness, density, efficiency and severance measures on spatial networks using either angular, Euclidean or custom metrics and link, length or custom weighting. Measures are localized using customizable network radius. We have found correlations between these measures and much real-world data ranging from vehicle and pedestrian traffic to land values and even health and community cohesion.
Best regards, Crispin Cooper (Sustainable Places Research Institute - Cardiff University)