blaze - Scala library for building asynchronous pipelines, with a focus on network IO. ZIO HTTP - Scala library to write HTTP apps. Powered by ZIO and netty and aims at being the defacto solution for writing, highly scalable and performant web applications. Http4s - Minimal, idiomatic Scala interface for HTTP services. tapir - Describe HTTP API endpoints as immutable Scala values. (Docs) sttp - Scala HTTP client you always wanted. (Docs) Scalatra - Tiny Scala high-performance, async web framework, inspired by Sinatra. (Web) decline - Composable command-line parser for Scala. doobie - Functional JDBC layer for Scala. ScalikeJDBC - Tidy SQL-based DB access library for Scala that naturally wraps JDBC and provides easy-to-use APIs. Skunk - Data access library for Scala + Postgres. Slick - Modern database query and access library for Scala. Allows you to work with stored data almost as if you were using Scala collections. (Web) Weaver-test - Test framework that runs everything in parallel. Noether - Scala Aggregators used for ML Model metrics mo. Lamp - Scala library for deep learning and scientific computing. It features a native CPU and GPU backend and operates on off-heap memory. sup - Composable, purely functional healthchecks in Scala. Monocle - Optics library for Scala. Skunk - Data access library for Scala + Postgres. Scala STM - Lightweight software transactional memory for Scala, inspired by the STMs in Haskell and Clojure while taking advantage of Scala’s power and performance. Scalaz - Principled Functional Programming in Scala. Matryoshka - Generalized recursion schemes and traversals for Scala. Scrimage - Scala image processing library. Fastring - Extremely fast string formatting. Finatra - Fast, testable, Scala services built on TwitterServer and Finagle. Freestyle - Cohesive & pragmatic framework of FP centric Scala libraries. Deequ - Library built on top of Apache Spark for defining "unit tests for data", which measure data quality in large datasets. Izumi - Ecosystem of independent libraries and frameworks allowing you to significantly increase productivity of your Scala development. Odin - Fast & Functional logger in Scala. Monix - Asynchronous, Reactive Programming for Scala and Scala.js. Coursier - Pure Scala Artifact Fetching. Twitter Util - Bunch of idiomatic, small, general purpose tools. scalameta - Library to read, analyze, transform and generate Scala programs. (Guide) Inox - Solver for higher-order functional programs. Stainless - Verification framework and tool for higher-order Scala programs. (Web) scodec - Scala combinator library for working with binary data. circe - JSON library for Scala. Ciris - Functional Configurations for Scala. ScalaPy - Allows you to use any Python library from your Scala code with an intuitive API. Treadle - Experimental circuit simulator that executes low Firrtl IR. Cats Effect - Purely functional runtime system for Scala. NewType - Scala with no runtime overhead. refined - Simple refinement types for Scala. uPickle - Simple Scala JSON and Binary (MessagePack) serialization library. LaCasa - Lightweight affine types and object capabilities in Scala. Spotted Leopards - Proof of concept for a cats-like library built using Dotty features. Izumi - Productivity-oriented collection of lightweight fancy stuff for Scala toolchain. (Docs) Libretto - Declarative concurrency and stream processing library for Scala. Natchez - Distributed tracing library for Scala. SWAN - Swift Static Analysis Framework. Chimney - Scala library for boilerplate-free, type-safe data transformations. banana-rdf - Library for RDF, SPARQL and Linked Data technologies in Scala. Scio - Scala API for Apache Beam and Google Cloud Dataflow. MacWire - Lightweight and Nonintrusive Scala Dependency Injection Library. Wire Signals - Small and effective event-handling library for Scala. Papa Carlo - Scala parsing library utilises incremental parsing approach. Avro4s - Avro schema generation and serialization / deserialization for Scala. Vault - Type-safe, persistent storage for values of arbitrary types. cats-retry - Library for retrying actions that can fail. Quill - Compile-time Language Integrated Queries for Scala. (Web) ZIO Optics - Easily modify parts of larger data structures. scala-typed-holes - Scala compiler plugin to emulate the "typed holes" feature of Haskell, Idris, Agda, etc.