I'm a lispworks user for a few projects. The killers, generally, for an enterprise project are the smaller binaries and java interface. I know of a few places that write gui apps in lispworks, but many (most?) projects with a user interface use some web framework stuff and only do the backend in lisp.
The java is a killer feature for lisp adoption. A lot of companies use java heavily and being able to easily interface with that stuff is often a technical requirement and if not a technical one, a management requirement.
- tree shaking and small binaries (±5MB a GUI app)
- the CAPI cross-platform and native GUI toolkit
- mobile platforme runtime (iOs, Android)
- its Java interface
- its KnowledgeWorks system for "rule-based, object-oriented, logical, functional and database programming"
- more?
ps: today we maintain a list of pretty decent libraries: https://github.com/CodyReichert/awesome-cl/