What Are You ‘allowed’ To Do With Open Source Software?

“Open source” just means the source code is available to look at, it doesn’t tell you what you can do with the software (that’s down to software licensing).
A better term is “free software”, which is licenced under what’s known as a free software licence. Not only is the source code freely available so you can see exactly how the program works, but free software can freely be copied, given away, modified, and used exactly how you want to with no limitations.
The only real restriction is that if you modify a piece of free software to create a derivative product, that product must also be distributed under a free software licence.
Open source software is not always free software, but free software is always open source.
Free software is different from “freeware”. Freeware is just software given away for free (that’s free as in “free beer”). Free software is software that you’re free to do whatever you want with, including copy it, modify it, give it away etc. (that’s free as in “freedom”).

I believe that the sky is open with Open Source Software, hence the word “Open”. You are free to do some incredible things, if you know what you are doing or really wreck havoc if you do not.

Anything you like !!!
And if you can help others, it,s a bonus for all to use !!
Everybody develops the system as it,s used which can make it more adaptable as an operating system or web browser like Firefox.

You can change anything you want, but should really give credit to anyone whose work you’ve used. Check out http://www.gnu.org/licenses/gpl.html

Modify it any way you want.