Scala 2 compiler and standard library. Scala 2 bugs at https://github.com/scala/bug; Scala 3 at https://github.com/scala/scala3
Haxe - The Cross-Platform Toolkit
Apache Groovy: A powerful multi-faceted programming language for the JVM platform
The Lux Programming Language
An artifact of fully-specified annotations to power static-analysis checks, beginning with nullness analysis.
Lucee is a high-performance, open-source CFML server written in Java. Supporting JDBC, Caching, Parallelism, HTTP, ORM, REST, S3 and dynamic Java integration, Lucee is great for developers aiming to build fast, scalable applications, delivering faster startup, rapid compilation and better runtime performance.
Slack Developer Kit (including Bolt for Java) for any JVM language