So I made a card game recently called Caliditas (that I should promote as revolutionary new take on the card game genre ).
In this card game the key attribute is the temperature of the cards. Every creature has a temperature and can only attack and destroy weaker creatures of the opposite element. Therefore the temperature attribute serves as combined attack and defence value. There is a more complete explanation in-game.
The game was made with Godot. The repository is here: https://github.com/V-ktor/caliditas (MIT license )
I added a very simple networked multiplayer mode, but you have to enter the IP address of the other player. I guess it would be better to have a match making option and a lobby and so on. However, I have no experience with running a server and how to implement it. There's also the problem that it would require a proper data privacy notice and so on...
If someone is interested, I also require help with artwork and ideas for new cards.