Discourse http://www.discourse.org
Mini Profiler https://github.com/miniprofiler/rack-mini-profiler
rbtrace https://github.com/tmm1/rbtrace
memory_profiler https://github.com/SamSaffron/memory_profiler
fast_stack: https://github.com/SamSaffron/fast_stack
flamegraph: https://github.com/samsaffron/flamegraph
Webpagetest: http://webpagetest.org
rblineprof: https://github.com/tmm1/rblineprof
General web perf tools and resources: http://samsaffron.com/archive/2012/03/23/sam-s-ultimate-web-performance-tools-and-resources
Sam’s blog: http://samsaffron.com
Jeff’s blog: http://codinghorror.com