typelevel/scalacheck

Property-based testing for Scala

milessabin/shapeless

Generic programming for Scala

scopt/scopt

command line options parsing for Scala

non/spire

Powerful new number types and numeric abstractions for Scala.

julien-truffaut/monocle

Optics library for Scala

typelevel/cats-effect

The IO monad for Scala

fthomas/refined

Simple refinement types for Scala

lihaoyi/fastparse

Writing Fast Parsers Fast in Scala

typelevel/simulacrum

First class syntax support for type classes in Scala

lihaoyi/utest

A simple testing framework for Scala

paulbutcher/scalamock

Native Scala mocking framework

japgolly/scalajs-react

Facebook's React on Scala.JS

scala/scala-parser-combinators

simple combinator-based parsing for Scala. formerly part of the Scala standard library, now a separate community-maintained module

lihaoyi/upickle-pprint

uPickle: a simple, fast, dependency-free JSON & Binary (MessagePack) serialization library for Scala

typelevel/discipline

Flexible law checking for Scala

lihaoyi/scalatags

ScalaTags is a small XML/HTML construction library for Scala.

scodec/scodec

Scala combinator library for working with binary data

typelevel/algebra

Experimental project to lay out basic algebra type classes

typelevel/squants

The Scala API for Quantities, Units of Measure and Dimensional Analysis

cb372/scalacache

Simple caching in Scala