For programmers it features a very flexible object model and is easily expandable - expect new modules in the future ! It is implemented in Java and the source code is available. If you want to implement your own web spider, the WebRobot class will be a good starting point. Even if you don't want to use it as a download tool but for indexing, link checking or whatever you want, JoBo is the right tool. Retrieving documents and handling these documents are completely seperated - therefore you can plug in your own module easily.