This cgishell simulates a command-line interface over HTTP, in your web browser. Use it on a server where you have CGI access (and Perl installed) but wouldn't otherwise have shell access (e.g. a commercial web host1), or if some draconian firewall prevents you from using ssh/telnet.
Allows you to do more or less anything on the system that you could do in a CGI script, without the bother of uploading and executing a script each time you want to do something that you can't do any other way. Since this is obviously not something you want the general public to be able to do on your server, it'll only run if AUTH_USER is set - i.e. if the user has authenticated with the server. You can force the user to authenticate and restrict access to certain users with .htaccess (instructions) or equivalent.
Since I'm trying to simulate state over a stateless protocol, don't expect to be able to do vastly complicated things - stuff like set won't work like it would if you were logged directly, and forget about anything interactive (i.e. any program that stops and waits for user input, such as more/less, passwd, text editors, etc.) - it'll just hang until the server times out and kills the process!
Important: This is the first (and only) version; consider it beta-quality only. It may or may not delete all your files (or allow someone else to do the same), give up root access at the drop of a hat, or crack the Pentagon and start World War 3. Getting it to work under Apache/Nginx/whatever is left as an exercise for the reader, but it works (or worked, when it was written) on M$ IIS with no problems.
Browser support: Mostly tested in Mozilla ("What's that, grandad?"), also works on Internet Explorer despite a bug with its implementation of .innerHTML (I've mostly worked around it, but tabs will display as spaces). It won't work in Netscape 4 ("What's that, great-grandad?") or earlier (no <iframe> support). Whatever you use, you need JavaScript turned on, and good CSS support helps too.
1 Before you ask, it's not installed on this server. Don't bother looking.