A recipe calls for Brown Ale, I didn't want to use beer, are there any substitutions?
No beer!? Hmmm.

Well, I can't think of anything that would give you the same flavor, and as a component of the dish it looms quite large...3 day marinade in beer? No way to replace that, and brown ale is distinctive and nutty. 

Beer and wine are natural tenderizers, which is what the marinade is for...They're some of the only ones that aren't acidic (buttermilk and yoghurt are others...Obviously not a good choice here) so filling that role without changing the character of the dish is going to be a serious challenge.

Are you looking for a non-alcoholic substitution, or just a non-beer one?

Since tomatoes and apples feature, you might try marinating in cider or tomato juice (depending on which flavor you want to push). You won't want to marinate for anywhere near the same amount of time: those two are acidic enough to digest your meat after 3 days. Might try apple cider and apple cider vinegar mixed. Vinegar marinated beef has an interesting twang to it.