A UWP MSNP client. As stated in the README it's possible to choose between MSNP12 and MSNP15. Managing your contact list and chatting are implemented in both versions, as well as features like nudges(no window shaking, just a notification) and ink.
MSNP was the procotol used by MSN Messenger, protocol versions mentioned above being used by versions 7.5 and 8.5 of the program, respectively. Though Messenger has been dead for years now, there's a server called Escargot that implements those MSNP versions and more, thus reviving both official and third-party clients, e.g. this one.
This was an MSNP and UWP learning project, as I was interested in both at the time. It is Windows-only, so the only compatible OS that doesn't have a better-functioning official client already is Windows for ARM, but even that is used by very few people.
The project was made in C#.