https://github.com/vygr/ChrysaLisp

Assembler/C-Script/Lisp 64 bit, MIMD, multi CPU, multi threaded, multi core, multi user Parallel OS. With GUI, Terminal, OO Assembler, Class libraries, C-Script compiler, Lisp interpreter, Debugger, and more...

You can model various network topologies with point to point links. Each CPU in the network is modelled as a separate host process, point to point links use shared memory to simulate CPU to CPU, point to point, bi directional connections. There is no global bus based networking on purpose.