Lucee is a fork of Railo, which was an open source alternative to ColdFusion (owned by Adobe, formerly Macromedia, formerly Allaire) which was written by JJ Allaire 20 years ago. I am sure most ColdFusion/CFML language docs would be pertinent to Lucee. ColdFusion was a rather prominent server side language in the late 90's and early 2000's. There are a bunch of companies that still use it today - I work for one. Overall though I would say it's widespread usage is on a significant decline. It can be very fast to get something up and running quickly but similar to PHP, can become a mess if one is not careful as you can freely mix data access, business logic and templating together.