Old cookbooks contain a wealth of ketchup recipes, tomato based and otherwise. Anchovy, walnut and mushroom ketchup varieties were popular in America long before tomato ketchup ever was. I've tried making some in the past and they were all yummy condiments, but no substitute for what we have all come to think of as "ketchup." The Heinz effect has really limited our scope! But there are traditional no sugar tomato-based ketchup recipes to be had in old cookbooks that might serve the purpose out there, too. I had one that got lost in a move in which the author prefaced his recipe by saying that in Maine sweetened ketchup is "regarded as an offense against God and man, against nature and good taste." It makes me proud to be from Maine, even though I still use sweetened ketchup from time to time.
I suggest you peruse the history and recipe sections in this book. Unfortunately the google preview leaves out all the non-tomato recipes (liver ketchup! blackberry ketchup! cockle ketchup!) but this question has totally inspired me to pick this up and hit the kitchen. Maybe not substitutes for ketchup per se, but it appears to be a Paleo-friendly sauce recipe book for us to usesauces activate!
