Metakit is a small, portable database library using a hybrid relational / hierarchical data model with a column-wise internal storage format. For C++, include a single header file and 125 kb DLL or statically link directly. Ideal for desktops, embedded systems, smartphones, and PDAs. Bindings for Python and Tcl. A very mature, stable code base.
Micropolis is a city simulation game engine based on the original classic SimCity source code. Micropolis is based on the Tcl/Tk version of SimCity. It consists of the micropolis module, which is the engine recast as a C++ class; the cellengine module, which is a cellular automata machine engine; and the tileengine module, which is a Cairo based tile renderer. It is intended to be used with the OLPC's Sugar user interface environment, but layered so the core code is useful in other contexts.
The Model Railroad System is a software package that can help you run your railroad. It allows you to operate your layout, from running trains to working your signals and switches. It has support for a network of Bruce Chubb CMR/I USIC, SUSIC, and/or SMINI nodes, and/or a network of Lenz's XPressNet DCC nodes. Azatrax USB-connected Model Railroad Detectors are supported. Software to create switch lists for freight car forwarding and create timetables for your railroad are included. There is software to help with photographing your trains, and to compute the correct value for those pesky dropping resistors for LEDs and/or incandescent lamps.
NaviServer is a versatile multiprotocol server originally based on AOLserver . It can be easily extended in either C or Tcl to create interesting Web sites and services. Main features include high performance multithreaded architecture, massive scalability and extensible approach, many modules, interpreted config file during startup, dynamic pages (ADP) in TCL, caching functions (static files and TCL byte code), pooled database connections, thread global arrays, introspection commands, mass virtual hosting that does not require server restart, a watchdog that restarts failed servers automatically, a telnet control port, efficient handling of down-/uploads, real-time upload progress/statistics, and more.
NetPlug is an extensible multi-connections, multi-protocol, network client program, written in pure Tcl/Tk. Includes a complete Irc client plug in that you should love if you like IrcII 'classic' look & feel (plus customizable style/colors scheme, sound,... Now includes full DCC support (with GUI), ircII like aliases and improved scripting (Tcl!), keywords (your nick...) highlighting, and more
OMNeT++ is a C++-based object-oriented Discrete Event Simulation framework, primarily targeted at the simulation of communication networks and other parallel/distributed systems. It includes a graphical network editor, a network topology description language, a rich simulation class library, multiple execution environments (both GUI and command line), a result plotting tool, detailed documentation, many sample simulations, and much more.