When I found out that the app I have developed basically in my free time to automate most of the monotone tasks that were needed at my first job, was being sold to customers as utility tool for our devices without me getting even a penny extra!

Absolutely illegal in France. Your company would probably get the IP, but they would have to pay you if they want to use it.
Check your country laws !

@willol most of it was developed at work though.. And I don't care anyway now.. I quit one and half year ago and started working for a startup which is basically competing bussiness and I work from home, get paid more and manage an entire software division.

So fuck them!! Ha