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: 
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.
Some timing diagram answers were listed [in this question](https://electronics.stackexchange.com/questions/3564/software-to-create-timing-diagrams). [TimingDesigner](http://www.timingdesigner.com/Docs/TD_datasheet.pdf) and [TimeGen](http://www.xfusionsoftware.com/purchase_timegen.html) were mentioned. Another is TimingDiagramer.