This lesson provided a very brief tour of a few popular web applications that you can use to go beyond building websites made up of static HTML pages. Not only are there lots of other applications out there, but there are lots of other categories of applications out there. You can find guest books, shared calendars, discussion boards, tools for sharing bookmarks, and everything in between. Also, even though I focused on applications written in PHP, there are equivalents of these applications written for many other platforms as well.
If you want to set up a wiki at work, and all your servers run Windows, you can use FlexWiki, which is written using ASP.NET. Its home page is http://www.flexwiki.com/ default.aspx. If you want a weblogging tool written using Java and JSP, you can use Roller, which can be found at http://rollerweblogger.org/.
Companies are always trying to bridge the gap between hosted applications that are very structured and applications you can download and manage yourself, which are generally more flexible. For example, a company called Ning (http://www.ning.com) has built a hosted system for constructing your own applications. It is "hosted" in the sense that your applications reside on their servers and you don't have to worry about logging into the servers or managing them in any way. However, they provide their own programming language and database that you can use to build applications. Their tools are not as flexible as languages such as PHP or ASP.NET, but they can still be used to build a wide variety of applications. It remains to be seen whether Ning's concept takes off, but the overall trend in web application development continues to move toward giving people with limited programming skills more flexibility in the types of things they can deploy without writing applications on their own.