Too many to list, some I built myself including the frame. I "do" ~ Human-Only-Pedal-Powered-Cycles, Human-Electric-Hybrid-Cycles, Human-IC-Hybrid-Cycles, and one Human-IC-Electric-3way-Hybrid-Cycle
How about a really fat tire bike - 155mm (6.1-inch) wide studded snow tires?
Currently I have a "ultimate trailer towing cargo bike" that I cobble welded together myself (ugly but it works) out of various old bike parts and a few car parts and steel tubing. It's an upright tadpole trike with double 26" wheels up front (With fat Hook-Worm tires mounted) and a single front wheel shock strut from an old 80's front wheel drive Subaru compact car with its bearing housing, stub-axle, hub, and wheel with full car size 155/80-R13 tire mounted with a full size hitch ball mounted right next to it so the trike can pull a full size car type trailer.
Works great for its intended purpose, but the other day I pulled off the summer tread tire it hand on the rear and threw on a studded snow tire I had laying around already mounted on an old 4-bolt subaru rim and tooled around my private road (lots of snow not that well compacted) and then out onto the county road (pretty well packed snow but with lots of ruts and stuff).
That small car studded snow tire on the rear sure did work well and I got plenty of traction and only spun out a little bit a couple times when trying to push both front wheels through fresh snow that put a lot of drag on them (not being single track trikes can be a PITA when cutting tracks in fresh snow). The gearing is set way towards the low end with a top gear only gives about a 2.5:1 drive ratio (where as the low gears are on the extreme underdrive end taking several rotations of the pedals to get on drive wheel rotation) on that rear car tire that is only slightly larger diameter then a 20" BMX wheel and noticeably smaller then a 26" MTB wheel so I wasn't able to get it up to a whole lot of speed to check out how well it handles at speed on some of the better packed and not-so-rutted sections of the county road but it seemed to do quite well even when hitting small ruts and wallows at as much speed as I could muster out of it (about 15-mph) considering its a big heavy tank and the low gearing its got.
So, long story short, I've got an idea in my head to maybe build a conventional two wheeled "Ultra Fat Bike" using two of these tires and rims front and back. Would have to build some custom hubs from scratch with some welded on four point star plates with lug bolts in each point to mount up the car type wheels and rims with their four bolt pattern (don't want to actually use a whole car front strut and stub axle and hub for weight reasons this time) but I think it could be done. Then I'm thinking buy a pair of "Cooper WeatherMaster" studded snow tires in that 155/80-R13 size which are some of the gnarliest studded snow tires I've ever seen available in compact car tires and it could make a heck of a winter bike for some of those big snow days. Obviously not the bike best suited to every winter day but there are days when a bike like that would certainly be useful.
What you all think? Especially you guys who have fat-bikes. I've never ridden a store bought fat bike before but all this talk about them and seeing a few of them riding around on the roads in town when I go into town along with the PITA of having to mess around with trying to ride rutted snow pack with my regular bikes just with studded snow tires on them on some days has got me to thinking and is what prompted me to try out that usually summer time only dedicated trailer pulling trike with a studded snow tire mounted for the big rear wide car tire on it (original purpose for being there to take the trailer tongue weights) and see how a big wide tire actually does in the snow.
Is going all the way up to that fat and big of a tire going too far? Yah, I realize the weight in the wheels penalty and you can feel it in acceleration it takes some "Omph" and muscle to get that big tire spooled up but once your moving it does act like a big flywheel and help keep your momentum up which did seem to help with busting through some of the small drifts across the road. Single track two wheels one in front and one in back front wheel being the only one that has to cut through fresh snow would have definitively helped make things better compared to all three wheels cutting tracks on my trike. I also think that wide of a tire would make just a two wheeled bike feel a lot more stable side to side when riding. I know some guys (check out the atomic zombie website) have built chopper bikes that use a big car tire for the rear wheel (which is partially where I got the idea to build my trailer pulling trike that way) and some have reported that they sometimes don't need a kick-stand to stay upright when parked because the width of the tire keeps them upright unless you push them over. That kind of tire width stability might be an asset in winter riding snow and ice slick stuff riding without having to resort to a trike or quad platform and having to cut more wheel paths through fresh snow.