The installer generates the extension GUI, the connection strings, the webservice web.config and installs the extension.
You can run the installer over and over again to generate multiple writeback extensions...
This is not open source, but a commercial product. It supports both QlikView and Sense, and both MS Sql and Oracle as databases for storing the data. The price for a full licensed version of this product is $4900 (unlimited usage within your company - which means unlimited number of writeback extensions).
jveldhoen It depends how you'd like to go about the data entry and write back. My initial assumption is that you'd need to create a mashup with input boxes or a table and take those inputs and create an XML or JSON ajax post to a web service and the web service could write to the db.
Send me a message with your contact details and I could help you get started.