Andean cultures didn't develop writing the same way we see among the Maya or other Old World civilizations. They did however keep records and store information via quipu ("khipu" - means knot in Quechua), which was created using a series of dyed, knotted ropes. Quipu likely predates the rise of the Inca and was used heavily by the Inca. Scholars go back and forth as to whether this really counts as "writing", but at minimum, they did record information (NY Times provides a good general description quipu and different takes on it).

Quipus (see here) can be read both horizontally and vertically. Furthermore, the different colors, twists, and arrangements of knots were also assigned meanings that were likely standardized such that the information could be "read" by different people. Some types of information contained in quipus include taxation, censuses, tribute tallies, and royal narratives.

Some additional resources on quipu:

• Mathematics of the Incas: Code of the Quipu
• Ascher and Ascher 2015