Juxt were very vocal about making Crux available beyond Clojure (can't find the exact quote right now, unfortunately). Perhaps the last time you checked it, any non-Clojure support was still WIP. However, since then they definitely have Java API available (Javadoc here: https://crux-doc.s3.eu-west-2.amazonaws.com/crux-javadoc/20....), as well as REST API (see https://opencrux.com/docs#restapi).
That's right, we're certainly keen to help all JVM users who wish to embed Crux, and for users sitting outside the JVM we have significantly more comprehensive JSON support and SQL queries in the works too.
Our upcoming SQL module is based on Apache Calcite which does a lot of heavy lifting and compiles SQL joins to Crux's native Datalog. For the curious: https://github.com/juxt/crux/blob/0f7d9c66db952a65efb4cba7e3...