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.
I think it comes down to the old "If you're not paying for the product, you are the product" idea. We like to think that if we're paying (anything) for something, then we are the customer and there is an implied contract between us and the vendor.
That's not to say that being a paying customer means a company won't also sell your data (just look at nearly every major retailer).
This really isn't what Foursquare is anymore. It's become a rather good location database & discovery platform.
I never used it when it was "hot" (~2012), but in the past few months I've really come to like it for finding places (restaurants, etc.) & making lists. Also, their tools for making edits to the DB are quite impressive, and they do a great job of leveraging superusers to moderate those changes.
Photoshop export (yes, even Save for Web) is notoriously inefficient. As others have mentioned here, ImageOptim (and the various command line tools it uses) can make your images significantly smaller (particularly PNGs).