Open-source developer Ching-Chun (Jim) Huang wrote in about the work he is pursuing with libx11-compat as a lightweight compatibility layer for X11 clients. For Xlib-dependent applications it can run without source code changes such as with macOS without XQuartz, Wayland-only Linux desktop sessions, headless CI environments, Android, and other non-x11-native platforms. The libx11-compat library is an in-process implementation of the X Window System client library and built atop SDL2/SDL3, SDL_ttf, and Pixman.
The code can currently run a number of classic X11 applications like XMosaic, Qt2 apps, XCircuit, XMMS, and more without an X Server.