Please Buy Me
No doubt about that, activeCollab is not an Open Source software in the sense I think about Open Source. But it is a well-crafted solution with professional support and it allows you to create your very own additions or plugins. And it is, to a certain degree, a business model based on trust: you can order activeCollab, download the source code, test it on your server and if you're not happy, you'll get your money back.
But can't you just tweak the source code and run it without a proper license? Sure. And chances are nobody will notice. For some 159,- € you can remove the activeCollab branding - and if you studied the source code a bit, you'll notice that you can also do so without paying. It's just … you shouldn't.
The fact that I have access to the source code gives me several advantages, since I can easily modify the behavior of the software or add new features - within certain limitations of course. And since the application is just pure PHP, without any encrypted or obfuscated parts, the installation of the activeCollab server is as easy as for any other well-designed PHP application.
There are other tools like Fire.app which are licensed under the GPL and let you download and compile the software without any charge. That is, if you know how to compile an Objective C application - and if you don't, you still have the convenient option to purchase the ready-to-go application.
When I switched to Mac years ago, I was surprised that I actually have to pay for small pieces of software I previously used for free on my KDE machine. On the other hand, I was now using well-designed applications which actually worked, were fun to use and were made by a small group of people making their living with just that application. While I do believe that big things can be achieved through voluntary work, there's so much more attention you can give to details if you know that you're family is fed.
I learned to enjoy paying for software, if it is nicely crafted, easy to use and backed by a small company with just the right spirit. Or to put it differently: just the opposite experience of buying Adobe Photoshop.