The Raspberry Pi is on the opposite end – it features a fully fledged operating system loaded on an SD card. It also has audio out, HDMI and RCA video output and an Ethernet port. This allows you to use your Raspberry Pi as a computer, complete with internet browsing, games and more. Plug in your keyboard, mouse and monitor, and you have an amazingly cheap computer.
The Raspberry Pi projects are more software based than hardware based. As it is simply a Linux computer, most projects are based around software hacks, media centres and graphics/sound and multimedia. It can however do some simple hardware control with the GPIO pins.
Raspperry Pi got different type of model, most commonly use was Rasperry Pi B Model.
The Arduino is a programmable microcontroller. The only functionality is what YOU program it to have. It is designed to read data from sensors, compute the data, and either send the data to a PC (or raspberry Pi), or output them to LEDs or LCD screens you have attached and programmed. By controlling relays, you can control high powered components via relays and control motors.
The Arduino is used is many different types of projects, from musical applications and interactive art exhibitions, to robotics and gaming gadgets. There are quite a few different types of boards for different projects.