Question: In EE all we need to draw some waveforms to ask or answer questions.

Is this could be done with TeX? Or what are the software's you people are using?

Could we have add some tools to draw waveforms in here?

Answer: 
Software I have on my laptop that can be used for this purpose includes: LTSpice, Scilab, Maxima, Inkscape - which has a nice function generator addin which can be used for quite complex waveforms, you just use a mathematical expression. It's under `Extensions->Render->Function Plotter`

![Inkscape Function Plotter](https://i.stack.imgur.com/OA384.png)

Math Functions Available:

![Inkscape Function Plotter Math Functions](https://i.stack.imgur.com/S95Qb.png)
For digital stuff, it's pretty easy to draw waveforms in a general vector drawing package like Inkscape. 

The trick is just to set up a reasonable grid and use snap-to-grid to keep your lines lined up.

I would imagine Visio and Dia have similar features.