A programming language that understands what a web app is
Wasp (WebApplication Specification Language) is a declarative DSL (domain-specific language) for developing, building and deploying modern full-stack web apps with less code. Concepts such as app, page, user, login, frontend, production, etc. are baked into the language, bringing a new level of expressiveness and allowing you to get more work done with fewer lines of code.
The Eta Programming Language, a dialect of Haskell on the JVM
...Eta's concurrency support helps you to build highly scalable systems. Eta has a strongly-typed Foreign Function Interface (FFI) that allows you to safely interoperate with Java. Eta has global type inference, giving you a dynamic language experience, but with a strong typing hidden underneath. Eta offers a wide range of strategies for handling concurrency including Software Transaction Memory (STM), MVars, and Fibers. Using the powerful and type-safe Servant web framework, we define our API as a type and the handler types for each endpoint are automatically generated and conversions happen automatically.