The famous X Windows benchmark program - now also available for Android.

Additional feature: The volume keys act as "throttle control".

It's more a toy than a tool, but at "full throttle" the number of revolutions per minute is kinda funny performance indicator...

Copyright notice:
Based on "xengine" by Kazuhiko Shutoh.

Permission to use, copy, modify and distribute this software, documentation, images, etc. is granted, provided that this comment and the author's name is retained. The author assumes no responsibility for lost sleep as a consequence of use of this software.