Compact Medium Format

A very nice 6x9 cm. folder with a coupled RF is the French DeMaria-Lapierre Telka III camera. It has a very sharp slightly wide lens, Sagitar 95mm/3.5. When they were sold new they used to come with a test negative. It's a little gem of a camera, though quite rare. I was able to enlarge some of its negatives 60x90 cm. with really good details. Highly recommended, if you decide on folders.

I used the Fuji 645 folder for many years with great success. I replaced the bellows once (Camera Wiz/Frank Marshman) and wish I still had it. Can't imagine a sharper lens and it slipped into a pocket nicely. I'm using a Bronica RF for that type of duty these days and the optics are top notch. Not as portable as the Fuji, though.

I can 2nd almost all of the folder recommendations, and will add an obscure thought of my own: 4x6 on 127 film folders! I have a couple of Agfa Billy Record no.0 folders, they are the size of an iPhone folded up and about twice as thick. The image size to camera size is insane. Plus if you're determined/crazy, you can stick a Heliar from a Bessa 66 on one! Voigtlander made some in this format, as did Balda and Welta (the Welta Gucki, the worst named camera ever).

My Fuji 645zi served me well for 10 years, and I bought it well used, but the LCD finally went as they prone to do. There are workarounds so I still use it occasionally.

Lomo LC-A 120. 38mm super wide lens (like a plastic SWC!), as small as an old folder and weighs about 300g.