Glidix is an operating system with a modular kernel, which mostly tries to implement the POSIX API, but is more focused on its own innovations. It has its own userspace with a full-fledged GUI, using its own object-oriented widget toolkit and compositor, "GWM". It even comes with a few games!
It currently uses ELF64 as its executable file format, and GCC/binutils as the toolchain. However, this is changing soon, with the introduction of its own format, and even its own toolchain!