On the regulatory side, for networks the NERC Reliability Standards for the Bulk Electric Systems of North America address similar concerns (including cyber security) in electrical grids. For highly integrated systems MILS kernels are an engineering solution e.g. to keep actuators and monitoring subsystems apart.

Some things that might not immediately turn up in google for "open source c++ numerical library" but maybe also of interest: symbolic computing GiNaC, or, into another direction, computational fluid dynamics finite element tools like OpenFOAM.

(Or more generally see the main Verisoft page. When posting on C verification perhaps one also should mention Caduceus)

Actually in Verisoft XT the successor of Verisoft now real C code is verified, including e.g. PikeOS with PowerPC assembly in a system developed to DO-178B airplane verification. In that project an important tool for C code verification is VCC developed by Microsoft Research, source included at that site.