An ancient / retro version of GTK and supporting libraries for fun. This is basically a fork of GTK 1.2.10 but modified a little bit to build on modern systems using CMake.

The purpose is really to build GTK 1.2.x applications on modern systems and not to target legacy distributions (after all, we're using CMake here). There is no guarantee that this even builds on anything non-Posix and probably requires a C99 (or higher) based compiler. It is only tested on Linux based systems.

If you are using a distro that still packages GTK 1.2.10 you should continue using that.

You first need to build and install glibretro on your system.

In addition to that you need some X11 development packages installed:

sudo apt-get install libx11-dev libxi-dev

The current project uses CMake to build the library:

mkdir build
cd build
cmake ..
make
make install

• Should I use this instead of GTK2/GTK3/GTK4/GTK5?

No.

• Why maintain GTK1?

GTK1 is a very small code base and is easily maintainable by a single person, especially since upstream is "dead".