However it's a broad term, ripple had purchasing power to secure ripple.com and associate the term ripple with their project, not sure the same could happen here, runescape is pretty well known
I think this is a very important point. You're not gonna get rune.com, and I doubt you will ever come up as the first result if someone searches for "rune" in google. All three options probably suffer from this same problem, except maybe secore (secore.com is not available and I imagine google will just autocorrect people to "secure"). For this reason I'll abstain from voting; I think this is a bad idea, given the options available.