Now my initial thought was to post about Ravelry... But I couldn't think of anything to say that hasn't already been said. If you've never used it, go check it out right now (then come back)!
Of course, once I'd discounted that, my brain went completely blank and just wouldn't come up with anything else beginning with "R" *laughs* So I shall use my approach for a previous uninspired post and list some interesting words again...
Rabelasian - coarsely hilarious (I like that there is a word for this)
Ragabash - idle, worthless fellow (fun word to say, although it doesn't sound very insulting, it sounds quite fun!)
Ranarian - froggy (I've never needed to describe something as "froggy" before, but now I know the proper word)
Rectalgia - pain in the butt (*laughs*)
Rejectamenta - rubbish/excrement (is it just me, or does it sound more like a spell from Harry Potter?!)
Reremouse - bat (I read it as ra-ra mouse, as though bats are just really fancy mice with a bit of pizzazz)
Resistentialism - theory that inanimate objects display malice towards humans (and any of us who have had yarn tangle for no good reason know that this theory is true!)
And to bring this back to knitting, check out this rug knit from rope.