Yes the Antikythera (sp?) mechanism one of those interesting historical finds. It was likely used for timekeeping and navigation based on what I know of it. Just because it was a long time ago didn't make people stupid. A few good examples along this line
Byzantine flamethrowers - 7th to 9th century very well made for the time, probably derived from the designs used in bilge pumps on ships though we don't have many of those and mostly estimate based on descriptions
Roman Iron Turtle seige mechanism - later Imperial period, a seige machine shaped like a pyramid on about two dozen wheels, faced in iron and wettened leather armed with a ram and scorpions, propelled by men pushing a capstan geared to the wheels
Archimedes Boathook - claw tipped crane used to snatch the rigging of boats attempting to lay aside a coastal fort and capsize them.
Steam Cannon - yes they really were invented as to how well the originals operated we aren't sure, but replicas using period materials have worked successfully
Automatic Ballista - whether they were made we don't know but we do have the design drawings and replicas using period materials show they work quite well
Egyptian Battery - highly controvercial, but it was obviously a battery and found in a metal-workers shop replicas have been used to electroplate metals successfully
Chemical Warfare - Chinese in the 4th century BC used Cyanide laced smoke on the battlefield at least once at it apparently caused significant casualties.
Roman mile-measurer - a cart with a mechanical odometer pushed by those building roads and setting down markers to measure distances.
Probably quite a few more I just can't pull off the top of my head.
