Windows/Mac/Linux: Mac users have long been able to easily make their own desktop apps of web apps using Fluid, but if you're not on a Mac, or you just want a command line approach, than Nativefier's worth a look.
Nativefier runs in the command line and once it's installed (you'll need Node first), you'll be able to turn websites into desktop apps with a single command from the command line. Just run this command and substitute the site you want to make in for
That's it. Nativefier will make a little desktop version of the website you enter. It's just a wrapper for the web page, but it's useful if you don't like having a million tabs open. Of course, there's also a ton of options you can run to customise the app, including means to add in icons, change the name or choose a specific default resolution. Fluid for Mac might still be a bit easier for most people, but this is a solid cross-platform solution either way.
Nativefier (Free) [NPM]