At DroidKaigi Reject Conference, I have talked about Okio, specifically the internal implementation of Okio, with @stsn_jp talking about the internal implementation of OkHttp. To describe it (maybe too) simply, Okio is a library for I/O and OkHttp is a library for HTTP+HTTP/2 client.
Both libraries are for Java and Android and applications, and both are the ones of the most famous libraries, especially in Android development.
* square/okio: A modern I/O API for Java
* square/okhttp: An HTTP+HTTP/2 client for Android and Java applications.
* Droidcon Montreal Jake Wharton - A Few Ok Libraries - YouTube
* DroidKaigi 2018 Reject Conference - connpass