NetQoS presented this evening at the San Diego Cisco User Group. It is an interesting product that competes with NetScout. It has a very cool web interface and seems robust, especially the overview NetQoS Performance Center which is the umbrella product that will aggregate SuperAgent, ReporterAnalyzer and NetVoyant.
There are some differences in their approach but the end functionality seems very on par. NetQoS does not make use of probes so it has some limitations on doing Layer2 correlation but their SuperAgent does application performance and the Harvester is a collector for NetFlow.
They are making use of IPFIX (new IETF name for Cisco's Netflow)* and IP-SLA (new IETF name for Cisco's Service Assurance Agent - SAA)* to do performance measurement from Cisco routers and switches. That is a unique aspect of their product.
* - corrected on May 31st, 2006 - Thanks John!