Mashups is a pretty broad term. A good definition for a mashup tool is a solution that allows developers to combine interesting data and then visualize that data through a web application

Usually, mashups are web applications that can be created quickly using standard web services (e.g., REST) and components (e.g., Widgets).

There are three kinds of Mashup tools: front end, back end and integrated. The differences are:

• Front end mashup tools: these tools help build web front ends like dashboards using widgets/gadgets and little to no programming (iGoogle, PageFlakes)
• Back end mashup tools: these tools combine web-accessible data and services into more useful web services that can be called easily using a REST-ful interface (Kapow, Yahoo pipes)
• Integrated mashup tools: these tools make it easy to build end-to-end web applications that link web widgets to data and services.

When evaluating mashup tools, you need to think about what kind of mashing you are trying to do:

1. Do you want to create a visual dashboard from existing widgets? Try a front-end mashup tool. These tools make it easy to create a personal dashboard that tracks your stocks, local weather, the time in 51 timezones and the current price of titanium.
   
2. Are you wanting to turn web-accessible stuff (like ebay auctions or linkedin contacts) into a web service API? Try a back-end mashup tool to get at data programmatically that you otherwise have to do by hand (and mouse).
   
3. Do you need to create an end-to-end web app like a dashboard or simple business portal? Try an integrated mashup tool to build applications quickly and with minimal programming. Integrated mashup tools are effectively the modern version of MS Access for the web.
   

Another factor to consider is whether you have to download and install anything to use it. Mashup tools can be purely web-based (like Yahoo pipes or PageFlakes), purely download (Open Kapow) or available both as a download or hosted (like WaveMaker and IBM Mashup Center, both of which are hosted on Amazon EC/2).

Here are five free, open source mashup solutions you might want to check out:

iGoogle - Front End Mashup Screen Builder Tool

If you are looking for lots and lots of widgets, look no further. iGoogle has tens of thousands of gadgets (many of the most popular ones NSFW, but that's how it goes). Try iGoogle here.

Open Kapow - Back End Mashup Service Builder

The web is a wonderful place to find information, if you are a human and have a lot of time. Getting programmatic access to data on the web is a completely different story (wouldn't it be nice to see which of your favorite restaurants has a table open at 6 tonight automatically?) Kapow is a web-based tool for creating "robots" that gather data on the web and return the results as a web service. Try open Kapow here.

Yahoo Pipes - Back End Mashup Service Builder

Pipes is a web-based tool that allows developers to aggregate, manipulate, and mashup content from around the web. It is not as full-featured as Kapow, but you can try it without having to download anything. Try Yahoo pipes here.

IBM Mashup Center - Integrated Mashup Builder

Mashup Center was written with the non-developer in mind. That design objective increases the number of people who can use the tool, but limits the complexity of what you can build. In general, Mashup center requires that developers create a set of enterprise widgets (using IBM's iWidget spec) . There is also a cloud version of Mashup Center, but it requires that you have your own Amazon account set up. Try Mashup Center here.

WaveMaker Studio- Integrated Mashup Builder

WaveMaker provides a fast and easy way to build web applications. It targets Java developers who want a RAD GUI builder as well as novice web developers who want to build web applications with minimal learning curve. You can try the cloud version of WaveMaker here, or try the WaveMaker download here.

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