One of the richest aspects of PBL is cooperating with teachers from other areas, schools, countries and with all sort of professionals whose area of expertise is somehow related with the project. Tackk offers a simple and easy way to help you find partners for your next project. Just post your idea with a sort description, telling who it is targeted for and wait for replies!!
Here is a brief tut to get you started.
And here is another to help you include a Google Form in your Tackk. You can easily include page breaks and base the order of questions on the given answers.
Hope you find the tools and the tuts useful!!