The startup I joined in 1999 had its own application server loosely based on AOLServer architecture.
We had Apache + mod_tcl, IIS with our own ISAPI extension, then in box connections for all major RDMS across all key UNIXes and Windows NT/2000.
Some left to join companies doing Vignette projects, others eventually created OutSystems redoing the same ideas, but with the newly released .NET.
However it was also a lesson in performance issues, and the constant pressure to rewrite Tcl code into C extensions.
Was great for rapid prototyping and a/b testing in volume. Not sure I'd pick it ever again for anything, but it was interesting for sure.
Some throwbacks of his from 1999:
https://philip.greenspun.com/wtr/aolserver/introduction-1.ht...
https://philip.greenspun.com/wtr/aolserver/introduction-2.ht...