The MicroDef (tar.gz file, 100 kb) is a 2D structural analysis code for frames. It has been designed for POSIX-compliant operating environments (it curently works on Linux, IRIX and Mac OS X with X11).
I have started the writing of this software because I wasn't able to find any existing open-source code that can fit my needs (I found the jBeam that is written in Java and thus unacceptable slow on my hardware and one program that uses Motif, but it is only available as a Linux/x86 binary and it require at least 1024x768 which makes it useless on my Linux laptop). There, of course, are some commercial packages but they are too expensive for home use.
The MicroDef is still unfinished, but it works (some thinks are still not very tested and they may include bugs). The code is written in the C language and it uses a Gtk+-2.x library for GUI and graphics. The graphics output (e.g. images) is available as a Postscript (see example) and as a PNG (it requrires the GD library.).
It is meant for small and simple problems so there are some limitations. It can't accept more than 300 elements (beams) and it is impossible to extend it (e.g. add any non-linearity nor thermal loads).