AFAICT Boost.Asio is still the go-to networking library. (Though Asio is also available as a standalone outside of Boost, I didn't know that until recently.)

Apart from that, Boost has quite a few goodies such as Boost.Json, Boost.Program_options, Boost.Interprocess, Boost.Lockfree, Boost.Unordered, Boost.Dynamic_Bitset, etc.

Some libraries, like Boost.Atomic, Boost.Thread, Boost.Chrono and Boost.Filesystem, simply became obsolete with modern C++ versions. In fact, they served as the blueprint for the corresponding C++ standard libraries.

Personally, I have been wary of using Boost in the past because it's such huge library, but CMake integration is actually quite good these days and I found it pretty easy to use. Documentation is also quite good IMO.

That is an interesting question. Here you can see the actual popularity of each library within Boost: https://grafikrobot.github.io/boost_lib_stats/. Also, see the comments at https://www.reddit.com/r/cpp/comments/130bzj8/has_boost_lost.... My company has been heavily utilizing Boost.Asio and Boost.Beast, so we've definitely reached for Boost in newer projects as well.

Boost appears to have become some kind of staging area for stdlib. Stuff that becomes popular in boost get eventually included in stdlib.