The Checks API is available for all GitHub Apps (the next-generation of GitHub integrations, see: https://developer.github.com/apps/), not just apps on the Marketplace. That said, I'm not aware of a Jenkins plugin that acts as a GitHub App (yet).
To be more accurate, your Mac isn't Linux, it's BSD. Luckily that *NIX underpinning is often enough to make it a solid development platform even when deploying to Linux.
It's not really BSD either; it's a mix of a bunch of stuff. The kernel XNU is a hybrid between Mach and BSD. I think there are also a few GNU utilities in the base system but I could be wrong about that (?)
I wonder whether "iPhone first" is really such a competitive position to take? (personally, I count it as hipster-ism) I would think developing for the Web should be easier and can reach a larger audience.