Since we switched to C++17 we can replace several boost constructs by their STL equivalent.
This includes, but may not be limited to:

• changing boost::regex to std::regex
• changing boost::optional to std::optional
• changing boost::variant to std::variant
• changing boost::filesystem to std::filesystem (note: this might have to be postponed due to Replaced boost constructs with their C++17 STL equivalents. #7263 (comment)) (tracked at Replace boost::filesystem with std::filesystem #13575)
• replace boost::program_options with CLI11 (suggested by @chfast at Drop support for old boost #4612 (comment)) (tracked at Replace boost::program_options with CLI11 #13574)
• check any other feature which is already part of C++17
• for Boost integer we can use the intx library (already seperate ticket: Consider using intx instead of boost::multiprecision (once stable) #3851)
• with regards to Boost.Ranges we should consider using ranges-v3 that are compatible with C++11/14/17 and is going to be part of C++20, too. (see Replace loops by range-v3 loops where applicable. #10738)
• replace boost::noncopyable with deleted constructor/assignments (Replace boost constructs with their C++17 STL equivalents. #7259 (comment))

Please Note:

Each of those changes should be done in its own PR.