I am talking about open source software like firefox, php and the likes. How do they earn from it? because it is really hard to believed that they just want to share their knowledge by creating very useful programs. Aside from giving them "donations" do you know how these guys earn from it?
There are a lot of ways ( support, custom builds, etc. ) to earn money through open source software / solutions but not everyone does it.
Open Source is more about reputation and trust rather than money, though you still get it through partners, selling commercial licenses, sponsors, and donations.
There are some who do customizations of open source applications for those who need such and they get paid for it.
Selling something that is related (and useful) to the open source software itself, i.e: Wordpress.com is selling hosting for wordpress. Since they're the one who develop it, they know how to use it better then others
Hm.. I'm curious too, but I do believe that open source programmers have their own way of getting paid by releasing their own customizations like what most have said.