[KsassPeuk]

For C, Frama-C + Eva plug-in does essentially the same job as Astrée (with small differences of support for specific features) and is open-source and freely available.

(There is an experimental C++ front-end, but it is not ready for industrial size C++ that makes extensive use of the standard library)

[zokier]

Frama-C is big reason why I think learning and writing C makes still sense in 2023.