The Eastern European Jewish immigrant sweet and sour sauce is mostly tomato sauce mixed with almost equal parts lemon juice and sugar, or at least that is how my grandmother did it. I have a recipe or two on here with that sauce

My mom was Filipina, and her original sweet-and-sour sauce for Filipino egg rolls (lumpia) was very similar to the NYT recipe linked to by nogaga. Next to the platter of lumpia, she always placed a custard cup of that sauce and another filled with white vinegar, a bit of salt and several cloves of peeled and smashed garlic.

Sometime during the late 60s, however, she got her hands on a "recipe" that called for a jar of baby food apricots (or peaches), a splash of soy sauce (always Kikkoman), some brown sugar, a splash of white vinegar equal to the amount of brown sugar, and a clove of pressed garlic. There were no measurements--she went by looks and taste. Our neighbors thought that that sauce was the best ever; I think we kids liked the NYT-style sauce better.

And then there are the Jezebel sauce variations: combine marmalade and horseradish. There are several here: http://www.food52.com/recipes/10736_jezebel_sauce. Or substitute plum sauce for marmalade for an Asian taste.

http://www.food52.com/recipes/11701_thai_dipping_sauce Oh it's great to have the daughter home from school! I thought this was more complicated to link!

I have a thai dipping sauce posted under my recipes (sorry--haven't figured out how to link ) that everyone loves..it is orange-y like the sauce we remember as a kid but nothing like the packaged stuff that's available now. we add the chili flakes because we like the heat, but you can leave it off.

This is a great recipe, very old, from the NYT archives. I think its a real winner. http://events.nytimes.com/recipes/1224/1997/12/21/Sweet-and-Sour-Dipping-Sauce/recipe.html?scp=8&sq=%22sweet%20and%20sour%22&st=cse

It is possible! Mark Bittman has a recipe in How to Cook Everything Vegetarian for ketchup-braised tofu. It might sound gross, but it is really just sweet and sour sauce, and super easy to make. You can make the same sauce and use it on anything.

two sweet & Sour sauce recipes from the Food52 database:

http://www.food52.com/recipes/4374_inji_currysweet_and_sour_ginger_sauce

http://www.food52.com/recipes/10460_sweet_sour_tamarind_sauce

Depending upon the cuisine that you're referring to.. Indian cuisine has a sweet sour sauce made from tamarind & dates, and other lesser known ones, such as a mango 'pachadi', in south Indian cuisine made with semi ripened mangoes & jaggery/ brown sugar. Commercial sauces made by Maggi are available as well...