Non-Linux FOSS: Mac2Imgur
I love to share images with people quickly. They could be cat photos or screenshots. Usually I post those silly images to Twitter and Facebook using Buffer, but occasionally, I just want to send a quick image to a single person. (This is usually when I'm trying to show my computer via screenshot.)
When I'm on a Mac, screenshots are really simple with the Command-Shift-3 keystroke. Sharing them used to mean dragging them to my Dropbox, and then finding the image and getting a public share link. It's cumbersome. But, there's a great utility for OS X called Mac2Imgur, whichuploads an image to http://imgur.com and provides a link in the clipboard. It even has options to remove the image after uploading, so you don't have 100 screenshots on your desktop. It's an incredibly useful utility, and it's completely open source.
If you ever share images from a Mac, head over to the GitHub page and grab a c opy (and yes, this screenshot is also on imgur here).