Haven't seen a post about this yet so I'll get the ball rolling.
In case you don't know, Tip of the Hats is a charity event hosted and supported by members of the Team Fortress 2 community. Since 2013, it has raised over $320,000 for Children's Oncology Services, Inc., which offers camps and other educational and excursion programs throughout the year that allow children with cancer to just be kids. With your help, COSI can offer attendance to kids at little to no cost to their families (copypasted from the site).
You can check it out at tipofthehats.org
The livestream is available at https://www.twitch.tv/tipofthehats and the stream is being done over the course of this weekend in three 12 hour livestreams, and today's is about 1/3 of the way through. So far it's raised about $60,000 (USD) and if you can't donate with money you can donate items through scrap.tf
There are also in-game items available as well as real world merch you can buy if you would like to support in another way. Some of the in-game items you can get are a $4.99 hat, as well as three different pins available through donating. There's also a pretty sweet t-shirt available until the end of the month for $25 at https://teespring.com/twitch/toth2016 (I'm looking to pick that up soon).
So if you're looking to do something to up your real-life karma, try donating FOR CHARITY!