TopBT (originally called Top-BT), is a topology-aware BitTorrent client implemented with open-source Vuze code base Version 22.214.171.124. It is developed as a research result from The Ohio State University. The "Top" in its name stands for "Topology" and it refers to the program's network topology-awareness feature. it actively discovers its network proximities to its connected peers by actively sending packets to those peers, and inspecting their responses. Through topology-awareness, TopBT aims to reduce unnecessary network traffic and at the same time, on average maintain its download speed. The paper "TopBT: a topology-aware and infrastructure-independent BitTorrent client" describes how it works.
The evaluation results of TopBT show it can achieve comparable download speed and at the same time reduce 25% download traffic on average.
For a comprehensive study of BitTorrent-like systems, see "Measurement, analysis, and modeling of BitTorrent-like systems"