The **join-calculus** is a process calculus developed at INRIA. The join-calculus was developed to provide a formal basis for the design of distributed programming languages, and therefore intentionally avoids communications constructs found in other process calculi, such as rendezvous communications, which are difficult to implement in a distributed setting. Despite this limitation, the join-calculus is as expressive as the full π-calculus. Encodings of the π-calculus in the join-calculus, and vice versa, have been demonstrated.

The join-calculus is a member of the π-calculus family of process calculi, and can be considered, at its core, an asynchronous π-calculus with several strong restrictions:

Scope restriction, reception, and replicated reception are syntactically merged into a single construct, the *definition*;
Communication occurs only on defined names;
For every defined name there is exactly one replicated reception.
However, as a language for programming, the join-calculus offers at least one convenience over the π-calculus — namely the use of *multi-way join patterns*, the ability to match against messages from multiple channels simultaneously.

The join-calculus programming language is a new language based on the join-calculus process calculus. It is implemented as an interpreter written in OCaml, and supports statically typed distributed programming, transparent remote communication, agent-based mobility, and failure-detection.

Many implementations of the join-calculus were made as extensions of existing programming languages:

JoCaml is a version of OCaml extended with join-calculus primitives.
Polyphonic C# and its successor Cω extend C#.
MC# and Parallel C# extend Polyphonic C#.
Join Java extends Java.
A Concurrent Basic proposal that uses Join-calculus
JErlang (the J is for Join, erjang is Erlang for the JVM))
C++ via Boost
These implementations do not change the underlying programming language but introduce join calculus operations through a custom library:

The Boost.Join library is an implementation in C++ within the Boost framework.
The ScalaJoins library is in Scala.
Joinads - various implementations of join calculus in F#.
CocoaJoin is an experimental implementation in Objective-C for iOS and Mac OS X.
The Join Python library is in Python 3.