Party animals and night workers alike are annoyed when the subway closes at night. Here's a complete list of subways that don't.
Those metros that close, why do they close at all? Many metro lines close for upgrade or construction work anyways, usually for several consecutive weeks, or even months, so that can't be the reason to close every night. The list below is evidence enough that all-night operation at least on weekends is technically no problem.
Keeping metros open at night will even save the expenses for staff locking and opening doors or guarding locked stations. For passengers going to ride home from bars or parties it means they can go without studying timetables, without digging into intricate details of night bus services, and without always watching the clock.
To be listed here, metros/subways, LRTs, or commuter metros need to operate at least every 60 minutes throughout the night at least once a week. (Most of them operate every 10 to 30 minutes, though.) Metro services on special occasions like New Year's Eve don't count, and replacement bus or tram services don't count as well, of course.