AOLserver is a multithreaded, Tcl-enabled, massively-scalable and extensible Open Source web server tuned for large scale, dynamic web sites. AOLserver also includes complete database integration and a dynamic page scripting language. AOLserver is the backbone of the largest and busiest production environments in the world including America Online's.

It has been ported to many Unix-derived platforms, as well as to Windows. A list is in the FAQ  under "What platforms does AOLserver support?"

Interestingly, some people classify AOLserver not as a "web server" but as an "application server." YMMV. Maybe it's best to classify it as a programming environment for generating dynamic web content under heavy load conditions?

 

In any case, AOLserver serves HTTP -- web pages -- containing the usual static files as well as ADP (AOLserver Dynamic Pages) containing TCL intermixed with HTML. The parsing and execution of the TCL code occurs "within" the server, rather than being transferred out through a CGI interface to another programming environment. The Apache web server running the mod_perl interface module for Perl scripting is about the closest comparison. The reduced overhead makes for better performance and allows for a higher maximum transaction volume (number of "hits") with the same hardware system.