We can see the application of a number of interesting formal verification tools and frameworks on Ethereum lately. In the event of rising attack vectors against the smart contract security model of Ethereum, formal verification has become a strong imperative. Initial efforts were based on Coq proof assistant. Nowadays we can see the adoption of K-framework and other powerful tools.
Ethereum 2.0 Beacon Chain has been formally verified using Dafny in the PegaSysEng/eth2.0-dafny repository. Runtime Verification has done an excellent formal verification of Ethereum Casper CBC Proofs recently. It is available in the following repository. There is also an interesting formal verification of Ethereum in Lem in the pirapira
/eth-isabelle repository. Lem is a language that can be translated into Coq, Isabelle/HOL, HOL4, OCaml, HTML and LaTeX. There is another interesting EVM Semantics GitHub repository that applies the K-framework based formal verification of Ethereum Virtual Machine.