Today is Pi day! The 14th of March, you know... 3.14 because nerds gonna nerd. Real nerds know it doesn't stop at 3.14, but goes 3.14159.... And so on. But that's beside the matter.
There is a currency called PiCoin, that can be mined without increasing your electricity bill. Instead of clockcycles, time is the thing that creates sparsity. You can start mining, then close the app, and it will continue to mine for 24 hours anyway. This is friendly both to the environment, and to your wallet. So download the app, and start mining for free today!
You can read about the theory behind the currency here:
https://minepi.com/white-paper
If you sign up using this link:
Then both you and I get extra coins when we both are mining. Give it a go if you like!