So I am about to start writing a manual for a piece of software. Are there any packages available to depict radio buttons, check boxes, tabs, menus etc.?
Though I don't know any packages that include symbols of radio buttons, check boxes, etc. I know some good GUI mockup software. I'd recommend using standard figures from mockup software, like the Pencil Project. It's licensed under GPLv2, and I think figures from mockup software are pretty straightforward. You could even use those graphics as inline images using a simple
raisebox ensuring correct vertical alignment like this:
During a long time, I used dpic language to generate primitive graphics. Xfig is working on Linux distributions to produce graphics with a GUI and is able to generate graphics to the PIC format, a format similar to dpic or gpic.
Years after years, I'm using more and more tikz/pgf but it needs more time to compile with some libraries. PSTriks is also a very good tool to generate graphics.
Symbols graphics or simple graphics placed precisely by entering their positions allow you to reach great quality figures. Don't forget that some documentations need to be printed in black and white, or just three colors. For graphics with full colors that stay also useful to adjust some colors with just few lines of code in LaTeX. With just few lines of graphics command in your (La)TeX code, all the figures of your documentation can change their style of drawing or their colors that why png or jpg are not all the time the best choice for illustrations but they are useful to generate quickly a result.