FileRunner is a two pane file manager for Unix and Unix like systems. It is simple and efficient and has a built-in FTP and SFTP client. It also does a reasonable (and improving) job on Windows systems. New and improved from a FileRunner of long ago.
ChemVisio is software which might be useful for educational purposes (non-organic chemistry, crystallography etc.). It might be a good visualization support for all people who need better illustrations than that you could see in books.
Open Source SIP Back to Back User Agent) and Billing system. Has an Embeded TCL interpreter making session control and session mediation limitless in flexibility. Useful for: Routing Engine, Calling Cards, SBC, Peering, Wholesale and more!
TkSftp - an X wrapper for the OpenSSH sftp console client
UnixConf is a System-Configuration-Tool for Debian(in future RedHat,SuSE,Open- & FreeBSD to) written in Shell-Script(sh/ash). It is a X/Dialog based Modular System-Tool created for Admins, to Configure your Base-System, Network, Servers,...
Small size template based websites
Rivetweb is a Tcl based engine for creating template based websites. Rivetweb maintains strict separation between content, representation and structure of the web site, it's template based, so you can easily change the XHTML/CSS code underlying your pages and produce a whole entirely re-styled web site in seconds.