Treo - Treo is the page speed monitoring tool that helps your customers from obtaining a faster web experience.
Raygun - Raygun gives developers meaningful insights into problems affecting their applications. Discover issues - Understand the problem - Fix things faster.
perf - Perf is a simple app monitoring solution paired with meaningful alerts.
Snare - Snare is well known historically as a leader in the event log space.
Pingdom - With website monitoring from Pingdom you will be the first to know when your website is down. No installation required. 30-day free trial.
Kafka - Apache Kafka is publish-subscribe messaging rethought as a distributed commit log.