Helios is a Domain Specific Language that compiles to Plutus-Core (i.e. Cardano on-chain validator scripts). Helios is a non-Haskell alternative to Plutus.
Helios is purely functional, strongly typed, and has a simple curly braces syntax. It notably supports closures, functions with optional arguments and multiple return values, OOP-like methods, enums as tagged unions, and generics.
The Helios library is written in Javascript, with complete Typescript type-coverage. This library lets you compile Cardano smart contracts and create Cardano transactions. Helios is all you need to build 100% client-side dApps for Cardano.