Monix is a high-performance Scala/Scala.js library for asynchronous, effectful, and reactive programming, consumed as a dependency rather than run as an application. It provides four core data types: Task (an asynchronous, cancelable effect with a trampolined run loop), Coeval (synchronous lazy evaluation), Observable (a push-based, back-pressure-respecting stream with a very large operator suite), and Iterant (a pull-based functional stream with primitive-specialized batch cursors). Alongside these it ships monix-execution (Scheduler hierarchies with trampolining/batching, a rich Cancelable family, cache-line-padded lock-free atomics, concurrent queues) and monix-catnap (MVar, Semaphore, CircuitBreaker, ConcurrentChannel, ConcurrentQueue, FutureLift). There is no standalone entry point; integration is via sbt libraryDependencies, and the build is a multi-module sbt project cross-compiled for JVM and Scala.js with shared sources plus platform-specific jvm/js implementations.
Fetch is a Scala library for simple and efficient data access, built on cats-effect. It provides a monadic abstraction (`Fetch[F, A]`) that automatically optimizes data fetching through batching, caching, deduplication, and parallel execution. Users define data sources by implementing the `DataSource` trait, specifying how to fetch individual identities or batches. The library then composes fetches using standard monadic and applicative combinators, transparently batching requests to the same source and running independent fetches concurrently. It supports custom caches, optional fetches, error handling, and debugging via a separate `fetch-debug` module. The architecture is a pure library with no runtime dependencies beyond cats-effect, making it suitable for both JVM and Scala.js. Key entry points include `Fetch.apply`, `Fetch.run`, `Fetch.runLog`, and `Fetch.runCache`. External dependencies are minimal: cats-effect, cats-core, and scalatest for testing.