Are you creating applications, which languages and libraries you use in Gameshell?
Since a game jam will be held, we plan to make one mini game.
I am considering the following
I would like to listen to your development environment and use it as a reference!
Hello @jun_3453,
I think there is no reference, it all depends on how you would like to code and if you would like to integrate your game into the existing Retroarch system. To integrate your game as good as possible, you could work with libretro. The whole system is based on libretro/retroarch, and thus it would integrate nicely into it.
Examples for libretro may be found here Libretro Examples and of course SDL is what you would work with then in C/C++.
I won’t have time for the jam, so good luck !
Thank you for your reply!
I will see the example of libretro later 
The Python Arcade Library is another option if you like game development via Python. Plus there’s a ton of example code on the website.