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.
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,...
TkSftp - an X wrapper for the OpenSSH sftp console client
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.
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!
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.
Schematic circuit editor for VLSI and Mixed mode circuit simulation.
Xschem is a schematic capture program, it allows to create a hierarchical representation of circuits with a top down approach . By focusing on interconnections, hierarchy and properties a complex system (IC) can be described in terms of simpler building blocks. A VHDL, Verilog or Spice netlist can be generated from the drawn schematic, allowing the simulation of the circuit. Key feature of the program is its drawing engine written in C and using directly the Xlib drawing primitives; this gives top speed performance, even on very big circuits. I have succesfully managed to simulate complete VLSI projects with this tool, both digital (Verilog / VHDL) and analog (Spice). The user interface is built with the Tcl-Tk toolkit, tcl is also the extension language used to send commands to the program. Schematics can be printed in SVG, PNG, PDF, formats. XSCHEM runs on Linux or other Unix-likes with Xorg server and on Windows with the Cygwin layer and required tools installed.
psDooM is a process monitor and manager for *nix systems. It could be considered a graphical interface to the 'ps', 'renice', and 'kill' commands. psDooM is based on XDoom, which is based on id Software's 'Doom'.