I have been watching the development of an open source replacement for Windows by Microsoft. It is called ReactOS. It is still in development. The latest version is 0.4.14. It is - per the site - still in alpha.
There is a forum there to talk about problems and other things related to it.
They have a 'shop' that has some nice ReactOS merchandise.
I have some older laptop computers that I will be trying it on. I think it would be great for older computers since it requires less resources to install and operate. Since it takes up less space and uses less resources, it could - potentially - operate faster than Windows. As it is in alpha development stage, there would definitely be problems.
It has been long in development and progress is really slow. It seems it has been in 0.4.14 for quite awhile now. I am looking forward to get farther along. One can help with its development at the forum at the site as well as other parts.
I am hoping to report on future development of ReactOS with this blog.