If you've been to Germany, you've likely seen roofs featuring this type of tile:

That's the Ergoldsbacher Karat tile, by manufacturer Erlus, and the design dates back to 1966. While it might not look special once installed, this ceramic tile is known for being particularly raintight, and you can see why by looking at both sides of an uninstalled Karat:

The ribs you see provide a triple-interlocking joint at top/bottom, and double-interlocking side joints. This next part is difficult to envision: The tile has been designed in such a way that at each corner, all four tiles overlap.

The design is so rain-tight that it can be installed on roof pitches as low as 7°.

Fancy hi-tech material? Nope, these are made of plain ol' ceramic.

Comes in five colors.