MKVToolnix announced that they were going to officially drop XP with version 9.x in 2015. Luckily, the next version v.10.0 was working on XP anyway.
Today I decided to update it after a while and I found out that it wasn't working anymore.
I took a look at the source code and luckily it didn't use anything weird and it was possible to compile every component targeting XP.
As to the UI, this one was tricky. The mkvextractgui hasn't really been modified during the latest commits and relies on old calls, so it was easy to compile.
As to to the mkvmergegui (mkvtoolnixgui), in the main branch it has been update to use functions available on Windows 7 only (not even Vista!).
I was kinda curious to see what they did and they basically broke Vista and XP compatibility with the GUI to implement some "fancy" W7 loading bars and a few totally useless stuff.
Anyway, I re-used the code from version 10.0 for the mkvmergegui ('cause it was XP compatible) and made it work with the new components and... guess what? It works.
It's gonna complain about a "mismatch" between the GUI version and the components version as soon as you launch mkvtoolnixgui, but just ignore it and use the program 'cause it's working flawlessly.
I just muxed a few .ts and .mp4 files into .mkv and it worked. I even extracted subtitles from a few .mkv files and it worked.
Let me know if you find bugs and please note that this is an unofficial version, so DO NOT update via the GUI and DO NOT report bugs on the official MKVToolnix site, but only here.
Link: https://mega.nz/#!eYE2hCrL!Z8k2l3OUC7wXxjJmI2KmtPh_wzEF_0mIMd56YivCweE