Web applications are very different than web sites. Web applications provide your customers with an online program rather than a desktop program. These can be for the company itself to use, or for your customers to use. Probably the most well known examples are Facebook and Twitter.
Most, if not all, of these web applications utilize what is known as AJAX, a method of sending and receiving data without having to refresh the entire web page. This provides desktop program functionality, or very close to it, in a browser.
There are many benefits to providing this kind of service, both to your customer and to you.
The user doesn’t have to deal with the nuisance of installing and updating software on a continual basis – all updates are automatic the next time they login; data is managed and backed up on a nightly basis from the web server as a typical free service; it doesn’t matter if the user is using Windows, Linux, Mac or anything else, the program still works.
There are times when a particular web browser doesn’t function as expected. It is easily resolved by using a different browser.