[peterbotond]

not often mentioned: tcl's slave interpreter, and command redirections from a slave interpreter to its master. a master interpreter can hold many slaves interps, and any slave can be a safe interpreter not execing anything that might be dangerous. redirecting, by renaming, a slave/safe interps commands the master will know. tcl's threading model (if needed): sending messages, one thread per interpreter, and one thread can have multiple interpreters. tcl-8.6 has a killer object model. tcl's vfs, and starkit/metakit makes distribution simpler.

what i do not use tcl for is: web. unfortunate lack of a framework.

it has good support for downloading stuff, ftp, http, bignums and algorithms if needed.