Back in May of 2014 I bought a Supernova from Kelly Starrett mobilitywod.com. I had never really used mobility aids in the past but had read about how helpful they were and it was too hard to get someone to rub my sore muscles (girlfriends expect you to rub theirs too, I guess).
My ‘little blue ball of pain’ has become a staple of my gym bag now. I use it almost daily for rubbing out those nasty knots in my muscles. The supernova works exceptionally well on calves, hamstrings, glutes, and those hard to reach spots in your hips.
The supernova is just larger than a softball and a little heavier, so it is super portable. At around $40 it is a must have for myofascial release and self help for mobility. I cannot recommend the supernova highly enough. Check them out at roguefitness.com and mobiltywod.com