Hyperledger Composer was an open-source development toolset and framework for building blockchain applications on top of Hyperledger Fabric. It was designed to simplify the development process by providing a high-level abstraction for creating and managing blockchain business networks.

Key features and components of Hyperledger Composer included:

Modeling Language: Hyperledger Composer introduced a modeling language to define the data structures, assets, participants, transactions, and relationships within a blockchain business network. This modeling language made it easier for developers and business analysts to design the structure of their blockchain applications.

JavaScript Integration: Smart contracts, known as “chaincode” in Hyperledger Fabric, could be written in JavaScript using Hyperledger Composer. This allowed developers to define the business logic of their blockchain applications using a familiar programming language.

RESTful APIs: Hyperledger Composer automatically generated RESTful APIs for interacting with the blockchain network. This made it simple to integrate blockchain functionality into existing applications or create new front-end interfaces.

Access Control: Hyperledger Composer provided tools for defining access control rules, ensuring that only authorized participants could perform specific actions within the blockchain network.

Testing and Simulation: Developers could test their blockchain applications using simulation tools provided by Hyperledger Composer before deploying them to a live network. This helped identify and resolve issues early in the development process.

Integration with Hyperledger Fabric: Hyperledger Composer was tightly integrated with Hyperledger Fabric, one of the popular blockchain frameworks. It simplified the deployment and management of blockchain networks based on Fabric.

It’s important to note that Hyperledger Composer has been deprecated by the Hyperledger community, and it is no longer actively maintained. The decision to deprecate Composer was made in favor of focusing on other Hyperledger projects and frameworks. Developers who wish to build blockchain applications on Hyperledger Fabric are encouraged to use other tools and approaches provided by the Hyperledger ecosystem.

As of my last knowledge update in September 2021, this information is accurate. However, the landscape of blockchain development tools and frameworks may have evolved since then.