"Paris traceroute" is a traceroute variant that detects different types of load-balancing approaches in the network, and tries to enumerate parallel paths. The (C++) source code is available under the GNU Public License (GPL). The code has been tested under Linux and NetBSD.
Avoiding traceroute anomalies with Paris traceroute, B. Augustin, X. Cuvellier, B. Orgogozo, F. Viger, T. Friedman, M. Latapy, C. Magnien and R. Teixeira, Internet Measurement Conference, October 2006, PDF