Learning to work on the BEAM with Erlang/OTP has been one of the best experiences I had in the past year, I used Joe Armstrong's "Programming Erlang: Software for a Concurrent World" book (and highly recommend it to beginners), I also heard good things about "Designing for Scalability with Erlang/OTP" (but didn't start this one yet), but nothing comes close to this in terms of depth.
The BEAM really feels like alien tech left from a highly advanced civilization and this book dropped in a such a great timing! Bought it right away, kudos to Dr. Erik Stenman for keeping it up after two cancellations!
What kind of software applications do you develop with BEAM/Erlang/OTP?
Right now they've been mostly toy projects, the more complex one being the back-end of an (WIP) MMO game (https://github.com/Dr-Nekoma/lyceum) and a couple handy libraries that I wrote myself (like https://github.com/dont-rely-on-nulls/migraterl).