With a little bit of hunting, and the right tools you can find out a lot about the website in question.
Obviously looking at file extensions usually gives you a good hint at the types of technology in use (e.g file extensions such as .asp or .php would imply the programming language in use, .html is used for regular HyperText Markup Language pages). You can check (or use tools to check) HTTP response headers, cookies, stylesheets, and comments in the source code to give you clues about the various technologies in use.
Here are a couple of the sites I used when I need to reverse-engineer me some information about a website.
You can use these tools to findout lots of useful bits of information, including:
- IP Address
- Netblock Owner
- Domain Registrar
- Name Server
- DNS admin
- Whois Info
- Reverse DNS
- Reverse Whois
- Email searches for whois records
- Search profile and rank information
- Visitor and Traffic Information
- DMOZ/Yahoo/Alexa/Compete/Quantcast Info
- Wikipedia Info
- Server Information (Web Accelerators/Reverse Proxies/Caching Servers)
- Analytics and Tracking
- Audio & Video Media
- Document & Encoding Info
So what do you use to find out more about a website?