window-swap.com
Let you check out the view from people's windows from around the world.
futureme.org
Let's you "send emails to the future you". It helps put into perspective how much has changed over the course of a year.
Boil the frog
An awesome site where you put add two music artists you like, and it creates a playlist connecting them.
Summary
1. radio.garden 2. window-swap.com 3. unsplash.com 4. futureme.org 5. Boil the frog