It's very niche, but the only thing I could come up with is Kvevri, a traditional Georgian winemaking vessel. They're sold today (and still used for their stated purpose, aging wine), I've personally seen kvevris with the exact same shape buried in a wine cellar of 12th century monastery, and at least going by the article they're like 8000 years old, and haven't changed much in that time.

My other ideas were:

• Bricks (turns out the earliest sun-dried mudbricks, which are very different from modern ones)
• Concrete (turns out it changed a whole lot since the Romans, modern concrete is much easier to pour, sets faster and is much stronger)
• Nuts & bolts (initially were hand-crafted and non-interchangeable - yuck!)
• Knives (I'll let knife enthusiasts speak about that one)