Awesome idea for a One Pager by Mike Bodge where you hit a switch to start mining cryptocurrency within your browser – all for a cause of your choice. You simply leave your tab open and the site mines Monero (XMR) on your behalf. Lovely touch with the favicon changing when you hit the switch and of course the "mining speed" slider to lower your hashrate if your fan is going nuts.
You've heard of Bitcoin? Well this is the same concept except you can easily "mine" the coins through your browser and we donate that money to charity. Leave the site open and turned on to your cause of choice and donate your spare CPU cycles to making them money.