Looks like a distant cousin of the crank I used to have. Probably the ring was mated to the arm off centre.

In other news, it is pretty likely that the ring will separate from the arm (well, develop play first...) sooner or later, especially if you're heavy and/or skid. Mine fell apart even though I'm light and never skid. These things don't stand up to brutal back-and-forth forces. Mind you, even the ultra-expensive CF cranks fall apart under brakeless fixed riders.

Long story short: best plan would be to get a new crank and transplant this one into a singlespeed bike where it could live longer. Or ride it into the ground and come up with a plan after that.

BTW, it's easy to check that the chain tension problem comes from the crank and not a bent rear axle. If the chain's loose/tight cycle is in synch with the crank rotation, it's the crank.