Free software for plotting bands around curves to show error margins

[ChrisVer]

I'm not really sure where this thread belongs...

Do you know any (free) program that can allow to build bands (instead of just line curves) to take into consideration the errors of a graph?

eg if I want to draw:
$y= bx + (c \pm \delta c)$ to get something like the yellow band in this (of course it's just an example for what I'm looking):

 

[mfb]

Looks like a science software question.

ROOT can do it, but I would avoid it if possible...

 

[gsal]

There probably are several programs that do it and probably several ways to do it...a quick search reveals that you should be able to do it using python/matplotlib with the "fill_between" plotting funtion; see this example.