How to find script software details about a website?

[MSL6600]

I need to find script details about some websites. I mean I need to know that Is that site made with Wordpress , Joomla , vBulletin or some other script. Some site I can easily find the details by viewing the page info on my Firefox. Some site I doesn't have that option. please see the below picture for more details.

I need to know the script software information about such kind of sites.

 

[Sonic]

easy.

only check the meta tags.

for example:
<meta name="generator" content="WordPress 3.1" />

wjunction meta tag is:
<meta name="generator" content="vBulletin"/>

right click and view source code.