I have a Raspberry pi and I find it is a fun, interesting and educational tool. It was designed by the Raspberry pi foundation and was aimed at children so they could learn more about computing, ict and programming in an easy, fun and enjoyable way. Amazingly,even though it is a fully-functioning computer it is extremely cheap. Budding inventors and pioneers are using it to control things like makeshift/homemade cctv cameras, laser cutters, 3D printers and robots. It runs on Linux* and costs £30/$35. It is about the size of a credit card and has two usb ports (although I would recommend getting a usb hub), it has an ethernet port, audio ports etc. unlike its predecessor which has no ethernet port (so no wifi) and 1 usb port. I hope this info has helped you on the decision of getting a raspberry pi or just info on the raspberry pi.
*Linux: an operating system (like windows or OSX etc.)