[doctorsher]

Both are quite similar at a high level. They provide generic utilities for improving synchronization, strings, random number generators, high performance containers, etc. Both are no stable ABI guaranteed, live at head encouraged.

At a more detailed level, I find Folly much more substantial than Abseil. For example, both provide high performance hash tables. Abseil also provides a BTree-based map, which Folly does not. But Folly provides concurrent skip lists, LRU evicted hash maps, a high performance MPMC queue, etc. And that's just talking about data structures. Folly also has asynchronous I/O tools, futures, reference-counted buffers for IO, and many other things outside the scope of Abseil.

Personally, I am loving the asynchronous I/O mechanisms in Folly. It feels more expressive and results in cleaner code than boost ASIO. Just a first impression though, I am relatively new to the library.