http://www.bonappetit.com/recipes/2013/07/cantaloupe-gazpacho
It's a Gazpacho we B's can enjoy, using cantaloupe.

Watermelon and peaches both substitute for tomatoes in recipes for salsa, for relishes, even for pizza.

Have you seen such replacements done particularly successfully?

Please tell us, here.

try jicama as well

I like my 'pacho made with pureed butternut squash ..... just the right consistency  

Right now enjoying on seeded flatbread:
Thinly sliced strawberries over shmeers of goat cheese.
Very tomato-esque.  Totally tripping the mechanism.  

I have also used pureed roasted red peppers with applecide vinegar in some recipes both in cooked meat dishes and as topping for pizza.

Even tart dark plums can work - especially in fresh recipes.

Don't know if you can have tomatillos, but they make a GREAT substitute for tomatoes in salads and tacos!

Thinly sliced nectarine is a great substitute for tomato on a brie-topped cracker.
Similar principle to my above finding re strawberries on goat cheese.
The slivers of fresh fruit supply the same consistency and moisture as good tomato, pairing equally well with cheese. A touch of fresh herb, such as mint or basil, can complete the experience.

Great at this time of year, when there are so many delicious fruits available in season; it beats looking longingly at the heirloom tomato displays...

lucky bum as I am tomatoes of all kinds are a superbene for me.... no tricky needs here for me at all...

I make a spaghetti sauce that my B husband says he can't tell isn't tomatoes.  But I don't know where the recipe is.  I just kind of do it now, without looking at a recipe.  If I can find it, I'll post it.  We all love it.

Quoted from Ribbit

I make a spaghetti sauce that my B husband says he can't tell isn't tomatoes.  But I don't know where the recipe is.  I just kind of do it now, without looking at a recipe.  If I can find it, I'll post it.  We all love it.

Interesting use of fruit, Ribbit.
Which fruit(s) do you use?

Not fruit...I use carrots and beets.  (Sorry, yes, I know you wanted fruits, but I thought I'd mention it.)  

Thanks to all who've suggested vegetables, but I was specifically soliciting experiences with fruit, as indicated by the title and the OP.

There have been many threads on the Forum on the subject of non-tomato "tomato" sauces (Johnny B. links us to Typebase's famous example), but this isn't one of them.

It's okay that others are not discovering this wonderful substitute.
Consider this thread, then, a spur to exploration amongst the fruits for very satisfying substitutes for raw tomato.