Gone Man’s Switch is a simple web application that allows you to create messages that will be delivered by email when you are absent (gone) for a certain period, AKA a dead man’s switch.
It is a free self-hosted alternative to deadmansswitch.net. It doesn’t have as many features, but it does the job.
More info in the GitHub repo: https://github.com/jhonderson/gone-man-switch
I have one set up to do several things for when it is my time, I made it fun and have a pop up box with questions, if you pass the questions it won’t activate.