Yakindu is a free integrated development environment to build Solidity-based contracts.
What is Yakindu?
Built by Andreas Mülder and others in 2018, Yakindu is an IDE for solidity that also has client implementation for other IDEs, such as Atom and the popular VS Code, facilitated by Microsoft's Language Server Protocol. It uses its statechart tool integrations to access core language features such as global variables alongside statechart modeling. Bugs are easier to spot and fix on Yakindu because it provides quick suggestions and fixes on the go.