This is not intended to be comprehensive or authoritative, just free online resources I've found valuable while learning more about Erlang.
- Erlang Master Classes (videos)
- Learn You Some Erlang
- Erlang in Anger
- Erlang Handbook: A concise reference for Erlang
- Concurrent Programming in Erlang / Part 1 (PDF)
- Try Erlang (hands-on web-based demo)
- Erlang for C, C++ and Java Programmers (very short overview)
- Thinking in Erlang
- Joe Armstrong's Ph.D. thesis (PDF)
- Introduction to Erlang blog series
- The Architecture of Open Source Applications: Riak and Erlang/OTP
- Getting Started with Erlang User's Guide
- OTP Design Principles User's Guide
- Official Erlang docs
- Alternative presentation of Erlang docs
- This site is particularly useful if you need to check docs for older versions of Erlang/OTP
- Inside the Erlang VM with focus on SMP (PDF)
- Erlang: The Movie
- Erlang is not a Concurrent Functional Programming Language
- Systems that Run Forever Self-heal and Scale: Lambda Jam keynote by Joe Armstrong
- Erlang's Open Telecom Platform (OTP) Framework: QCon talk by Steve Vinoski
- Erlang – A survey of the language and its industrial applications (PostScript)
- Why Erlang Is Awesome
- When would you choose Erlang?
- Erlang's Big Idea
- Solving Embarrassingly Obvious Problems In Erlang
- More Embarrassingly Obvious Problems
- Programming Rules and Conventions (incomplete)
- Joe Armstrong on GitHub and Blogspot
- Jesper L. Andersen on Medium and Blogspot
- Paolo D’Incau
- Takeru OHTA (Japanese)
- See also http://qiita.com/sile
- Ward Bekker
- History of Erlang
- One Pass Real-Time Generational Mark-Sweep Garbage Collection (1995)
- The development of Erlang (PDF)
- Implementing a functional language for highly parallel real time application (PostScript)
- Erlang - A survey of the language and its industrial applications (1996)
- An Introduction to Core Erlang (PostScript)
- Bjarne Däcker's thesis (2000)
- Comparison of Erlang Runtime System and Java Virtual Machine (PDF)
- Testing Erlang Concurrency with QuickCheck
- Note: QuickCheck is commercial software, but tremendously powerful and accessible as a web resource via QuickCheck CI
- Actor Model of Computation: Scalable Robust Information Systems / Hewitt, 2012 (PDF)
- The Actor Model (video)
- Actors and Continuous Functionals / Hewitt & Baker, 1977 (PDF)
- A Universal Modular ACTOR Formalism for Artificial Intelligence / Hewitt, Bishop, Steiger, 1973 (PDF)
- Actor-Oriented Models for Codesign (PDF)
- ACTORS: A Model of Concurrent Computation in Distributed Systems / Agha, 1985
- Relation to Pi Calculus from
erlang-questions - Modeling Erlang in the Pi–Calculus (PDF)
- π-calculus (Wikipedia)
- Erlang Cookbook: collaborative code snippets at ErlangCentral
- Mostly Erlang (podcast)
- Erlang interviews and resources
- Akka team blog
- Why Do Computers Stop and What Can Be Done About It? / Gray, 1985 (PDF)
Twitter seems to be the de facto water cooler for technical conversations, and Erlang is no exception.
There are far more active accounts than I can comfortably list here; these are just a few of the more interesting ones.