We integrate with QuickBase as a read-only data source, which required some finagling to deal with the QB API's auth mechanism. The work we did could be used by anyone. I haven't seen any demand for this, so either it's niche or people have solved it some other way, but I thought I'd write it up and post it anyway:

https://isa.its.yale.edu/confluence/display/SN/QuickBase+into+ServiceNow

Cheers,
bw