Let me introduce a nice, easy to use, free and open software made to draw diagrams in seconds. Support layers, can group items for easier work, and have a huge palette with predefined symbols for various type of diagrams. It's called Dia, and works fine on Windows, Linux or Mac OS.
Some useful palettes:
Electric, Circuits
ER, Database, UML
Cisco, Network
Flowchart
Engineering diagrams [Chemical-, and Civil engineering, Cybernetics]
@Reefania, Feel free to ask if you have any question regarding this program.
Btw, a quick tip for everyone, select a tool while Shift is pressed, and that tool will be enabled until change. (Useful if you want to draw many lines/shapes.)
This tool is very useful ! Now I'm using it on my projects and presentation Thanks Kane for this, I'll be needing some guide from you and I got some question too, Exploring is Fun
It's a big help I need this one to play with xD