A great project to work on is building a weather station. The Raspberry Pi 2 has so much processing power to offer:
It can store a large amount of data in a database with ease
It can be its own web server running with a variety of programming languages
It can crunch numbers, create statistics, and eventually become nice graphs
It can even stream live videos using WebRTC or RTSP
Atmel AVR (used on Arduino) and PICAXE are very well-known microcontrollers that run code with real-time precision. The advantage of these microcontrollers is that you can program them with simple code once, upload the code, disconnect them from the development board, and use them like a standalone IC.
Your initial cost for a development board maybe about the same as a Raspberry Pi on its own, but after this, getting the programmable Microcontr oller Unit (MCU) will cost a few dollars, and will be even cheaper for tiny versions.
There are expansion boards available for...