In many applications, you need to track an object. One simple method is color based tracking. I have developed a simple tool for that with OpenCV. All you have to do is just to adjust the High and Low values of HSV slider in the left window till you filter the image and you only see your desired object, here I'm tracking a green pen, a blue water container, and a red bottle top. The code is pretty easy and straight forward but I found different pieces of the codes for each part all over the internet and I change them and adapted them together so they can do the job.
The code on my GitHub account.