Splashy - Breathtaking, auto changing wallpaper app for macOS, Windows, Linux, iOS & Android
Future Me - Send an email to your future self
Splashify - Beautiful desktop wallpapers for Mac and Windows
Letter to Yourself - Send a physical letter to your future self
Irvue - (previously Unsplash Wallpaper) Gorgeous wallpapers on your Mac.
Letterflix - Send letters and snail mail online to the USA, Europe, India, or anywhere in the world. Letterflix is the easiest and secure way to send letters and snail mail anywhere in the world from the comfort of your home.