Four, three of them rideable.
The un-rideable one is the old Repco mountain bike that I had in the late 90's as my all-rounder to get me to and from primary school. Un-rideable, because the frame is now too small (probably was then too). Otherwise it goes.
I bought a Dahon Boardwalk later, I was initially using that for commuting combined with public transport, then it extended to day trips. It has a 105kg load limit, which given I'm about 95kg, that's a bit limiting. So I started to think about what I wanted, and one day, when taking the Dahon back to the shop to get a recurring problem fixed, I snapped and bought a new one.
The one I bought is a Giant Boulder 26". I specifically wanted a bike that could go off-road, and was looking for something that had front suspension and disc brakes. The Boulder was what was suggested to me. I bought that in early 2010, and it's been my commuter ever since. I swapped the original knobbly tyres for semi-slick road tyres, later the mechanical disc brakes were upgraded to hydraulic brakes (because I kept fraying front brake cables; 3 in the first 10 months) and in general, that was my go-to when I wanted to go out on a day trip, commuting was still on the folding one.
Over time I started riding the Boulder more often. I bought a trailer which was handy as I was able to put the folding bike in that, ride up to the bike shop, hitch the trailer to the folding bike, drop the Boulder in and ride home again, no need for catching the bus when servicing was due. I didn't like commuting on the fold-up bike at this point, and so I started to look around again. The Boulder does okay off-road, but with the semi-slicks, is set up for road use. (Some would say I should consider a hybrid or road bike, but I appreciate the lower-range gearing of a mountain bike.)
Finally bought the Talon 29 ER 0. Initially I was looking for a dual-suspension mountain bike for touring purposes. The need of a rack and available options forced me to the Talon, which was suggested when I asked the local shop as the dual-suspension models didn't have the mounting holes for a rear rack. It's now my back-up commuter and my long-distance ride. I plan to do some touring with it in the future, just not sure where at this point.
The Dahon now only sees action when one of the other two needs servicing, and one of these days I should consider getting the Dahon serviced. I don't see me buying another bike for now, I've got enough to get by.