EMBARK is a small kernel, designed for educational projects. It has very limited scope and is designed to be extensible.
I am using the riscv-gnu-toolchain, configured with --with-arch=rv32im --disable-linux --disable-gdb --disable-multilib and built using make -j <number of threads>.
You can build the kernel using make kernel. Make sure the toolchain is in your path!
You can use the package.py script to package a kernel and multiple user binaries into a single img file.
Debugging information is also emitted, it's a json formatted file called <name>.img.dbg.
To generate such an image, run python3 package.py out/kernel <user bin 1> <usr bin 2> ... output/path/memory.img. You can edit the script to change various variables. They atre somewhat well documented.