Forum OpenACS Q&A: Response to pure-TCL OpenACS - first release
Currently it's a stock tclsh installation - I'm using ActiveTCL 8.3 on W2K ... since it just runs the installer code (no web pages), it's basically just a big shell script without any multithreaded dependencies.
I'll need to worry about threading with apache/mod_dtcl and potentially with tclHTTPD, but not with FastCGI. The idea behind FastCGI is that you can have a bunch of CGI scripts potentially reliant on non-multithreaded libraries, but your web server pre-spawns them into multiple waiting processes to eliminate the normal CGI startup overhead. Each waiting process only handles one request at a time, so you don't have threading issues.
Because of this, I'm operating under the assumption that I can ignore threading and still have OpenACS running under tclHTTPD for development and FastCGI as a reasonable deployment option.