Shaft

Anarchists have rigged the Fenton building with bombs, and it's your job to dismantle as many as you can before they go off. Each bomb is represented by a timer, which counts down in 10-second intervals. You'll have to scramble your way through the 21-floor building and find them all in time; you can either take the stairs, or call the elevators. Problem is, the troublemakers have rigged the elevators, too: when you exit, they go right back down to the lobby. To make it worse, all the doors are stuck open... so if you don't tread carefully, you may quite literally get the shaft.

The number of bombs is selectable (up to 20), to vary the challenge level. The game is shareware - registration gives you the option to adjust the bomb timers, from the 10-second default to a range of 1--60.