I like using PHP, good community support, and yes it is free. I would be difficult to hide the source code. I have read about a compiler that the Facebook people put together but I am not sure if it would hide the source good enough to be safe.

Postgres is a very good database that can be free. I personally don't see a reason to pay the fees for a commercial database. It is that good. If you need support then you can use enterprise db which is not free.

>what are the advantages besides they are free?
>If i sell an application in php they can see my source code?