Stuart Williams explains vert.x: basic idea and architecture, how it uses Java's NIO and async APIs, how it allows using various JVM languages (Groovy, JRuby, Scala, etc), the EventBus and much more.
Rich Hickey explains the basics of Datomic, its approach to transactions and query, Datalog, CAP, ACID and BASE, and much more.
Bob Lee explains the popularity of Java, future language features like Lambdas, DI with Guice vs. the Dagger framework, the role of Java vs. Ruby at Square, hiring at Square, security and much more.
Debasish Ghosh talks about the advantages of functional programming and how its abstractions help to reason about code, Monads, DSLs, NoSQL and MongoDB, and much more.
Ken Little talks about scaling Tumblr to keep up with their blogging users: scaling the data model, sharding, their PHP frontend and the Scala backend, and much more.
Rich Hickey explains how immutability enables Datomic's features and facilitates programming (not just in functional languages). Also: Datomic and other NoSQL stores, Clojure Reducers and much more.
Stuart Halloway explains Datomic, programming transactional behavior with Datomic, Datalog and logic programming, programming with values, Clojure Reducers and much more.
Phil Trelford discusses how to design large scale applications with functional concepts, the state of the F# community and much more.
Rúnar Bjarnason talks about the ideas behind and features in the popular scalaz library, programming concepts like (bi-directional) lenses, Scala Macros, and much more.
Miles Sabin explains dependent typing in Scala, the Shapeless project that demonstrates these concepts, static typing improvements in Scala and Scala Macros.