Yes: fixed-gear mountain biking, just like the Pass-Stormers of the 1930s...
- As a training aid to get that pedalling soupplesse.
- To save on brake pads, during the winter, however I still ran a front brake.
- Winter mud-sliding fun.
- Fixed gear on a MTB will climb climb climb. Forget about riding downhill at speed, go for control and a leg workout instead.
- Run a slicker tyre on the back. This will help to pop a skid on gravel and slide on leaves.
- Gearing: run a 1-2 cog smaller for speed. So 34:16T instead of 32:16T etc.
I have been riding fixed gear off-road on and off for 7 years putting a sprocket onto a 6-bolt disc rotor hub. This was for training and also to add a bit of excitement to my boring commute from Brixton to Croydon. I used to find all the parks in Streatham Hill, Norwood and Tooting Bec.
I rode fixed a few times in the Peaks by accident and found it was incredibly satisfying on a solo ride if you know the terrain.
I have been riding a pink 29er around Friston Forest in Sussex but have found a 26" is easier to skid and control.
Have fun and be safe. Fixed riding is supposed to be controlled and effortlessly stylish. Well, I dunno whether I ever attained that but I have had some fun battering myself.