MollenOS | modern operating system that is built with focus

Fully prepared docker images with a toolchain installed are provided from valios/vali-toolchain. This repository comes with a Dockerfile that you can use to build the OS with. You can also include the userspace by downloading the build .tar file from the userspace repository and keep it in the same folder as you run the docker command. Then docker will include it when you build an image file. Building the OS with no artifacts.
depends.sh
checkout.sh
build-cross.sh
Remember to check out all the submodules with the command git submodule update --init --recursive. The last step is now to run the depends.sh script that is located in this repository which installs the final pre-requisites (nasm, dotnet, cmake platform script). The script is located in tools/depends.sh. After this, you are essentially ready to start developing on the operating system. When/if you make pull requests when contributing, please follow the pull template that is provided.
Just building this repository is not enough for the full OS experience. You need to checkout the userspace repository that contains C++ runtime and applications and build those as well. For this you need to have the SDK/DDK installed (make install - remember to set CMAKE_INSTALL_PREFIX when configuring) and the appropriate environmental variables' setup. Then the command make install_{img,vmdk} will automatically pull in all built applications and libraries into the OS image. Then follow the instructions located here to get the sources for the applications.
These are highlighted build configuration options for the cmake generation, there are more options, but these are the most often configured.
There is a series of build commands available.