I've been using Instapaper for a long time. Typically, I read the stories I save to the service it one of my tablets. There's an app for that. There is, however, no dedicated Instapaper application (although the service can be accessed by a wide number of RSS readers) that allows me to get into my Instapaper account on my MacBook.
"What's the matter, Bellamy? Firefox not good enough for you?"
No, it is not: I receive notifications from a number of websites on a regular basis. When I'm reading, I don't want to deal with that shit.
The best solution for getting around this, that I've found so far, is Fluid. It's a free app (although it has enough utility that you really should spring for the $5 unlocked version) that lets you transform any website into a standalone application.
Getting your own, custom app sorted out, couldn't be easier: download the app, install it and let 'er rip. You'll be asked to enter the URL of the site you want to create an app for, its name and where you want to store it in your computer. Fluid will even grab the website's Favicon for you, so it looks snazzy in your Mac's dock.
I have no idea of how secure any passwords or information plopped into a Fluid-made app might be. As such, I don't plan on creating a Protonmail app with it any time soon. But for a low-risk service like Instapaper or Google News, it's a pretty sweet deal.