Does Ubercart have an external API? Does Ubercart have an external API that a 3rd party site could query? Specifically from a fulfillment point of view? We need to be able to query the system for items to ship, then update the order's status and set a tracking number after the item shipped. All this is done on a completely different server/company, so needs to be done via a publicly exposed API (like a REST or SOAP service). Does Ubercart do something like this?
Ubercart does have an API (see http://www.ubercart.org/docs/api and http://api.ubercart.me/ ), but I don't see general REST or SOAP support related to fulfillment.

Some options may include miniRESTapi or as noted UCServices and Bee Colony for Drupal 6. There are some vendor-specific SOAP implementations for CyberSource, but I do not know how well-supported they are.