Burr Gherkin
Impressively productive compared to my cursed cucumbers and for something with a leaf like a watermelon. Actually, Cucumis anguria, had some competition from the citron for pumping out the fruit this summer. I would grow it again if I could figure out what I can do with this bounty of little fruit. Perhaps... gherkins?
My source: Seed trade from down south in the U.S. I hope to have some available this year.
Achocha
Stories of Cyclanthera species impressive productivity in mild climes such as the UK did not come true in the sand trap of the old garden or during our mini drought, interspersed as it was by storms. I can confirm that it is a very impressive climer however.
My source: Seed trade from a mild part of Europe.
Citron
Want to surprise your friends with your prowess at growing watermelons? Try the perserving melon: citron, Citrullus lanatus. You can't split this baby open and dig out juicy goodness unfortunately but you can prepare all manner of canned yummies. Mostly they are for a lemon preserve but I have heard of them being used in place of cucumber and apple. Currently on my research list as you can see I have a few dozen. Anyone want to try one?
My source: Perth Seedy Saturday
Gourds - exotic up here
They aren't ripe yet but they're trying. I'll have to update you further on how they are doing. Langenaria siceraria is pretty enough to grow as a decorative especially as its large white flowers open later in the day.
My source: An italian squash and gourd mix
Mouse Melon
I didn't get a chance to grow Melothria scabra year but I they get tops for cuteness and have a nice flavour the one time I did try. They were grown in shade so descriptions of vines dripping with little melons was inaccurate for me. I'll try them again before throwing in the towel.
I'd love to hear other people's experience with the cuke pretenders and other unusual edible gourds and melons.