The Berkeley Open Infrastructure for Network Computing (or BOINC) is a way for you to get involved on global research projects. You install a client and then the slack time of your particular machine is used in the networked task of crunching numbers. You may have heard of SETI@home which is a collaborative effort to analyse radio telescope data in the search for extra-terrestrial life. Gus over at PiMyLifeUp has written a great, current tutorial on installing and configuring the BOINC client. You can read it here.
Here’s a massive project for you. Normally, pool automation systems cost somewhere in the region of $10k. So, an Instructables user decided to create his own using a Raspberry Pi. He hooked up all the inputs for the main swimming pool and the adjacent spa pool to relays and then had the Pi control them. He then built a web interface for it to enable him to control and set-up the two pools via his smartphone. 60 hours and a comparatively minor $1000 later, he had a fully working system. You can follow an overview of the project on Instructables
Mike Moyer was tired of seeing Samsung commercials for the Family Hub refrigerator with the built-in camera and decided to make his own using a Raspberry Pi, a webcam and a light sensor. Every time the fridge is opened, the Pi takes a picture of the contents. He used a buck converter to take the fridge’s power supply down to 5V for the Pi and also created a website where the last picture taken was published. You can see the current picture on the website here. Mike’s done an explanation video which you can see below and you can visit YouTube for a bill-of-materials (check the video description). The Python program he wrote is available here.