Bluepill is an open source tool from LinkedIn for running iOS tests in parallel on multiple simulators with great reporting features, and extra reliability features.
Bluepill runs tests in headless mode for less resource consumption, automatically retries when a simulator hangs or crashes, packs tests into groups automatically based on running time, generates reports after each test run, and reports stats based on currently running stats.
This image from the readme shows Bluepill in action:
You can find Bluepill on Github here.
A great tool for iOS testing.