Ryan Huber wrote and open-sourced a single file web app called flashpaper for sharing secrets. Here's a version of it I've deployed - it's public to the internet, anyone can create a secret and share it via a one-time-use link:
Flashpaper is great if you have a trusted server and a trusted operator running it. Seriously, don't use a random flashpaper server on the internet if you want to keep your secrets secret.
https://flashpaper.logsnitch.com
Here's Ryan's code:
https://github.com/rawdigits/go-flashpaper