A Russian gun designer has developed an ingenious conversion kit for the AKS-74U or AK-74M that allows it to be switched from a conventional layout to a bullpup configuration on demand. You could call it a “Semi-Bullpup” configuration. When the stock is unfolded it works just like a regular rifle (see below), but when the stock is folded a trigger forward of the magazine can be used to fire the rifle.
This conversion is not just two trigger on the same rifle. When the stock is folded it disconnects the rear trigger and the front trigger is connected to the firing mechanism. The trigger blade is then lowered into position. When the stock is unfolded the reverse happens.
The system also includes dual iron sights, one fixed set for use when the stock is unfolded and a flip-up set for when used in the bullpup configuration.
The patent for this invention can be viewed here (in Russian)
Many thanks to Max Popenker for the information and photos.