[pwaring]

I suspect it's likely to be:

RoR: Large number of contributors with relatively small patches, few full time contributors who are paid just to work on RoR.

Linux: Possibly smaller number of overall contributors but supplying more patches each, and more patches in total. More contributors who are paid to work on the kernel on a full or part time basis.

[tonfa]

The numbers for the kernel are well known (and they are hard to beat for any open source projects): https://lwn.net/Articles/395961/ (for every version ~1.1k devs and around 10k changesets)

[jgesture]

Indeed. I don't recall the exact numbers, though I've heard both Linux and RoR numbers, I think that Linux has factors more developers committing to it than RoR.

Linux is, perhaps, the most rapidly changing piece of software in existence