GHIRL is the Graph-based Heterogeneous Information Representation Language: a java library for representing, querying, and navigating graph- or network-based data structures.
TraffStats: network Traffic Statistic - is a monitoring and traffic analysis software, using SNMP to collect data from any enabled device. - has the ability to generate graphs (using jpgraph) with the option to compare and sum up different devices.
Webstats is a set of centralized open-source scripts that use PHP and MySQL to create a log containing various statistical information about website visitors and to record and analyze this data using text and graphs.