Do you consider it as weird if I thank the open-source community in the acknowledgement section of a paper?
I also mentioned technical forums and Q&amp;A sites (about GAMS, C++, the GNU Scientific Library, LaTeX, Maths, Statistics..., in my case) in the acknowledgement section of my PhD memoir.

I do not really think that doing the same in the acknowledgement section of a paper is inappropriate. As long as it is expressed in the same terms as other acknowledgements, I actually think it is a good and revolutionary idea.

Of course, all the coauthors of the paper should agree in including that kind of acknowledgement, just as it would/should be regarding other acknowledgements.



UPDATE

To expand and complete my answer, I should say that, in my humble opinion,


the 'Acknowledgements' section of a paper is not usually mandatory;
in case there is one, it should be kept not too long;
you can mention anyone or any 'entity' you are thankful to;
if there are too many people or 'entities' to mention, try to select the most relevant ones;
you may consider to keep some place for sort of formulaic or routine acknowledgements such as thanking anonymous reviewers, etc.


But, of course, there should definitely be a place for the 'real' acknowledgements. If you are really thankful for the help from online communities, or you just want to highlight it, I think there is no problem. For me, it makes no difference with other 'personal' acknowledgements, such as thanking some concrete colleagues for reviewing a draft of your paper, for instance.