Talking points about open-source software

[Nemanja Milosevic]

Hello fellow ambassadors! :)

As discussed in our EMEA meeting, I will be invited (most likely) to a Microsoft
conference here in Belgrade, Serbia (1000+ developers are expected) to hold a presentation
about .NET developer toolchain on Linux. It will be a great opportunity to promote Fedora
and FOSS. The Fedora part I got covered, and I know what I will talk about. Mostly about
how Fedora plays nice with many developer tools, how developer friendly in general it is
and how it's fantastic with the frequency of tools updates. Also how nicely it
integrates into some of the already existing Microsoft Services (like Azure)

However the second part about open source software - I'm stumped. Does anyone here
have any talking points or prior presentations experience on trying to "sell"
the idea of FOSS to someone who is only making proprietary software? It's a pretty
hard topic and I would love to hear some of people with greater experience in promoting
the FOSS way of thinking than myself.
  
I just have no idea on where to even start. I thought about talking about some great open
source libraries for .NET developers and that would be fine since I am using many of them
and have only had great experiences with them, but than comes the issue of licensing and
selling open source software as a part of a closed software solution. Most of the
mentioned libraries are GPL licensed if I remember correctly so you see what is the
issue.

So in short, how would you present greatness that is the FOSS philosophy to developers who
make a living on selling custom-made business/enterprise software.

Any insights, tips or materials would be greatly appreciated. 
The conference is about a month away, and I think this is an interesting subject even if I
don't get to present it. :)

Thanks in advance to everyone.

Cheers!
Nemanja