BizTalk Server provides an extensive library of out of the box functoids. In case you need functionality is not offered through the existing functoids you will need to built your own custom functoid. However there are quite a few available customized functoids available you can reuse and save you the time of building it yourself. This article provides you as developer all the resource available regarding custom functoids for BizTalk Server.
This list is intended to be a knowledge base of all Custom Functoids that are available:
Another important place to find a huge amount of BizTalk related articles is the TechNet Wiki itself. The best entry point is BizTalk Server Resources on the TechNet Wiki.