Xming: free X Window server for Windows
The X-Win32 license received from MIT expired last week. So I installed
Xming, a free replacement. It is licensed under
GNU GPLv2, so technically speaking we should be able to get the source code. Unfortunately, the source code is not distributed in a download-friendly way, e.g., packed into a single file. Indeed, we can find something on http://www.straightrunning.com/Xming/, but it could be difficult to download all of them (without using a suitable tool), and I did not attemp to get it. Also what's available there seems to be of the latest version. Not sure how to obtain the codes for the previous releases.
Despite all the issues with the source code, it works well on my laptop, as long as the Xming-fonts package is also installed.