Plan 9. Seriously. One person can understand the whole OS including the kernel. File servers coupled with 9p provide an excellent abstraction for distributing services across networks. Source code is included and the build system is designed with cross platform baked in OUT OF THE BOX.

All you need is a driver for the switch chip that serves it as a set of files you can read and write configuration commands to. With the right driver setup you could then configure the chip using human readable textual commands and use a script and standard cmd line tools to configure the switch. We could PXE boot plan 9 and leave the switch diskless. PXE booting plan 9 networks is brain dead simple and works out of the box.