Existing operating systems like Linux and Windows are very huge and have a lots of redundancy. For example in Linux there are many different GUI frameworks avaialble. Also the user has the choice between hundreds of programming languages likes Fortran, C, C++, pascal and so on.
A possible minimalist alternative to Linux would be realized in the Forth language which can be executed on a GA144 Forth cpu. the main advantage of bare metal stack machines is, that they have low register count which results into an energy efficient design. The major cause why Forth is not very popular in computer mainstrea is because it is much harder to program than C. Even with a good tutorial, it is complicated to write down instructions into forth. Even a register based assembly language is easier to explain than Forth.
But this single bottleneck can be solved with a high level language interpreter, for example a BASIC interpreter which is encoded in Forth. There are some examples available from the past. The idea is to write a program in Forth and this program is able to execute a BASIC program. The main advantage is, that newbe programmers are not forced to type in the routine in Forth, but they can do in a normal BASIC dialect.
Let us summarize the idea of a Forth operating system. The kernel is written of course in Forth because this code gets executed with the maximum speed on a stack machine. The kernel has access to the hardware including the graphics display. High level programs like a text editor, a hello world program or a prime number generator are written in BASIC which is executed by the basic interpreter. This ability makes it likely that a larger audience is interested to write new software or port existing software to the Forth operating system.