is pygame used for games only? or it is used for some application like traffic simulation?
can we produce a slide bar in pygame?

Pygame can be what you make of it. It is very suited to games certainly. It is very efficient at moving things around and taking events, though its harder to write applications in, its really not meant to apps.

But traffic simulation. I reckon that that could be done rather well. Just make the right classes and start of with some pyGame tutorials to learn the basics of it and there you go!

And yes you would be able to do a slide bar game in pygame as well, as i said. Just learn the basics first.