Many of the netizens haven't heard of Google Apps. Some of them are aware of it.

Google Apps is the best Application that helps to maintain your own domain. (You should have your own domain to use it).
The best part of it is, Google Apps is a free edition.

With Google Apps one can get

• E Mail for their own domain which will work same as GMAIL. For the E Mail from a normal hosting company it will charge at least 600Rupees per year.
  
• Talk for chatting in between domain users as well as other conventional GMAIL users
  
• Docs and calendar applications for customized domain
  
• Google Pages for creating web pages to the domain name.
  (Normally in domain hosting there will be two charges, one is domain registration and file hosting,
  For domain hosting it will be less charge like 4$ per year and for file hosting it will be around 20-30$ per year)
  
• Google sites may be very less people have heard about this. This is a feature for Google Apps users only…. With this feature we can create as many internal sites as we can.
  This feature is similar to sub domain.
  

Advantages:

• Unique concept of giving all the required applications for a domain at one place including file hosting.
  
• With the Google sites, it is easy to maintain different sites for different fields with in the same domain
  
• It is a free application
  
• One can create up to 500 users (it can be increased by requesting more) with free applications
  

Disadvantages:

• Google pages gives 100MB of web space to host for your site, but you can't create any folders to organize
  

• Google sites gives an option to write blogs with in the site, but it lacks RSS support.
  

Competitors:

As for my knowledge, Microsoft is the only competitor in similar application (Live Domains) which provides only mail and messenger at this moment.

What If one doesn't have own domain but want to use Google Apps????

With Google Apps Team edition, one can sign up with their school or company mail ID and start using Google Apps. You can't use your personal mail ID's for this purpose.
This option will not give you any mail account, since it shall be approved by your IT admin, but it gives you a option to login to Google Talk with your official mail ID (school/college/Office) and chat with your Google friends

Google Apps although has some limitations, for a small business users and personal website owners it is very helpful.