This plugin trades higher RAM usage for lower CPU usage (and thus shorter execution times, where RAM is plentiful) when running RSpec. It does so by explicitly taking control of when Ruby can run a GC cycle – enabling you to allow GC runs on only every Nth test.

See Careful Cutting to Get Faster RSpec Runs with Rails for more details about this project. This technique is one of several employed to produce significant performance wins for common Rails project structures.