The R.Y.N.O (short for Rip You a New One) is a man portable, auto targeting multi launch rocket weapon, and the most powerful weapon in the game. It can be obtained from the black market dealer on planet Rilgar, in the downtown area, and costs 150,000 bolts.
Getting the bolts together to afford it can take a while, but it's well worth it. There are three ways you can get enough bolts:
1) Just keep visiting different worlds
2) You can also lots of bolts by participating in hoverboard races on Rilgar and at the Gadgetron HQ track. In the races, you get 1K bolts for improving your score (by doing tricks) and 1K bolts for improving your time. So start by doing a slow race and 1 trick. Second race go a little faster and do an extra trick. Keep going a little faster and do 1 extra trick every race. Each race will there for net you 2K bolts.
3) You can use the Rilgar hoverboard track glitch over night to earn a load of bolts. Just see the video linked to see how its done.