IMO, it has the best ergonomics among scripting languages for embedding into native applications. I'm using it as a serialization format for a game, with the JimTcl interpreter. It's easy to create fluent hierarchical structures that straddle the line between code and data:
Similarly, I have a early-stage JS library for hierarchical statecharts. It revolves around nested contexts and an explicit message passing interface for controlling states between parent/child/sibling. Example:
https://github.com/msteveb/jimtcl