The app is http://discrete.li/ it's basically analytics service for ajax requests. Website owners plant a small javascript snippet in their site, and I track all statistics, including latency tracking and payload logs.
The service is pretty simple right now, but it is reliable. I use it for 6 months to track a medium-size app in production. I don't expect people to pay right away. I'll give it for free in exchange for feedback + patience while I implement it :-)
any way, I would love to hear your thoughts....