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.
VisualVM - VisualVM is a visual tool integrating several commandline JDK tools and lightweight profiling...
StatusCake - Website Uptime Monitoring & Alerts – Free Unlimited Downtime Monitoring
OProfile - OProfile is an open source project that includes a statistical profiler, capable of profiling all running code at low overhead.
Better Uptime - We call you when your website goes down
MemoryLogic - MemoryLogic offers tools to add process id and memory usage in rails logs and to track memory leaks.