If you're familiar with the Raspberry Pi and you like it, there's a good chance you'll like the Arduino, too. At first glance, the two devices are very similar to each other, but there are some key differences between the two devices. The Raspberry Pi is essentially a mini computer that you can take out of the box and start on new projects right away. The Arduino is a circuit board that you'll program to perform certain tasks, and what it does will entirely be up to you.
You can make it do all sorts of things, ranging from creating a smart garbage can, or making your own traffic light. It'll require a bit of work, as it doesn't simply work out of the box as a Pi would. Going back to the garbage can example, you'll need a sensor, jumping wires, and a motor to make everything work. On top of all that, you'll need to program the device to do what you want it to do.
If you pick one up out of curiosity, there will certainly be a learning curve to it. With plenty of guides and tutorials available, you should be able to get started on something small, and work your way up from there. Once you learn what the Arduino can do and your skills improve, you'll find many uses for one. At the very least, it can become a fun hobby for side projects.
Why should you get an Arduino?
Anybody looking to pick up a new hobby, and learn some programming and tinkering skills while doing it, will benefit greatly from an Arduino. If that sounds like you, and you have around $50 to spare, then you should pick one up. It's definitely best to start with a smaller project in mind, like a smart garbage can, and work your way up from there. As you begin to learn more about the various boards, microcontrollers, and other add-ons you can get, then you can tackle larger projects.
This is a hobby, much like the Raspberry Pi, that can get expensive quickly. The cool thing about it is you can start off cheap, and learn as you go. The Arduino comes with open-source software written in Java that will make creating code for a project easy, as it'll run on Windows, Mac, and Linux operating systems.
You'll be working in a special environment that highlights features for you, creating an environment that makes it harder to make mistakes. Once you're finished with the coding, you can put the code onto your device with a single button press. You'll get as much out of this hobby as you put in. It can be an interesting way of bringing various things to life around your house, or it can be a simple way to blow a few dollars on a new experience to try out.