Mobile performance testing platform from akamai based on the webpagetest.org infrastructure, free. Useful.
Airbrak collects error messages from Ruby on Rails (and others via unofficial plugins) apps and collects them for review. Looks interesting. Starts at $5/month up to 4 projects, 4 users, 15 errors per minute.
Siege is an http regression testing and benchmarking utility. It was designed to let web developers measure the performance of their code under duress, to see how it will stand up to load on the internet.