Working with text is annoying sometimes, especially when you're copying-and-pasting something with wonky formatting. Boop is a free and open source Mac application from developer Ivan Mathy. The idea is to paste text in here, transform it in some way with just a few keystrokes, and then copy it again in whatever app you're using it in.
This is a little hard to grasp, so let's talk about an example. If you have a chunk of text that's all capital letters, and you wish it wasn't, you can paste the text in this application apply the "Downcase" script to change it over. In an instant, your text will be in lower case.
You can choose a script using the keyboard shortcut, CMD+B, or you can click the Select your action box at the top of the window. A pop-up box allows you to search for a script, browse using the arrows, and hit Enter to apply the script to your text.
If you want to get an idea of the scripts that are offered you can open the pop-up and type an asterisk—you'll see a complete list. You'll also notice a lot of scripts that are related to programming, which is the real target audience of the app. I think it's useful for writers too, though. My personal favorite scripts do things like remove unnecessary line breaks, convert color codes, and replace smart quotes.
And there's also a collection of custom scripts, which are easy to install—you just need to set up a folder for scripts in the settings then download the scripts you want to use to that folder. The best one I found can convert CSV-formatted tables into markdown; another one can turn any string of text into a hashtag.
This is the kind of application you probably won't open often but will be thankful for when you do. That's the best kind of application, in my opinion: something that does a few jobs very well and doesn't ask for your attention otherwise. Note that there's a ported Linux version, in case you're not a Mac person.