uPickle: a simple, fast, dependency-free JSON serialization library for Scala
ScalaTags is a small XML/HTML construction library for Scala.
Macros for simple/safe RPCs between Scala applications, including ScalaJS/ScalaJVM
Scala/Scala.js library for manipulating Fancy Ansi colored strings
Programmable, Typesafe Document Generation
Pretty-printing value, types and type-signatures in Scala
An experimental library for Functional Reactive Programming in Scala
Acyclic is a Scala compiler plugin to let you prohibit circular dependencies between files
OS-Lib is a simple, flexible, high-performance Scala interface to common OS filesystem and subprocess APIs
A simple testing framework for Scala
Cask: a Scala HTTP micro-framework
Provides the geny.Generator data type, the dual to a scala.Iterator that can ensure resource cleanup
Tooling around scala-js
Scala library providing "source" metadata to your program, similar to Python's __name__, C++'s __LINE__ or Ruby's __FILE__.
Writing Fast Parsers Fast in Scala
A Scala port of the popular Python Requests HTTP client: flexible, intuitive, and straightforward to use.