"Conflict-free replicated data type" https://en.wikipedia.org/wiki/Conflict-free_replicated_data_type
"A comprehensive study of CRDTs" http://hal.upmc.fr/inria-00555588/document (original CRDT paper by Shapiro, Pregui, Baquero, Zawirski)
"CRDTs: Distributed Semilattices" http://blog.plasmaconduit.com/crdts-distributed-semilattices/
"Replication: weak consistency model protocols" http://book.mixu.net/distsys/eventual.html (section "CRDTs: Convergent replicated data types")
"Synchronization in a Distributed System" https://blog.8thlight.com/rylan-dirksen/2013/10/04/synchronization-in-a-distributed-system.html
"Why vector clocks are easy" http://basho.com/posts/technical/why-vector-clocks-are-easy/
"Why vector clocks are hard" http://basho.com/posts/technical/why-vector-clocks-are-hard/
"Interval Tree Clocks" https://github.com/ricardobcl/Interval-Tree-Clocks
Roshi by SoundCloud https://github.com/soundcloud/roshi
"From the Ground Up: Reasoning About Distributed Systems in the Real World" http://bravenewgeek.com/from-the-ground-up-reasoning-about-distributed-systems-in-the-real-world/
"Readings in conflict-free replicated data types" http://christophermeiklejohn.com/crdt/2014/07/22/readings-in-crdts.html (further readings)