CIAO is the Chandra X-ray Center software developed for the analysis of Chandra data. Chandra is the first astronomy mission to have many independent pixels in a 4-dimensional data space (position[2], time & energy), and so required more generic software to handle the full information content. CIAO is non-mission specific (apart from a few instrument tools), supports multiple data formats, and follows OGIP conventions for all FITS files. You can find more information in the Introduction to CIAO Tools and Applications.

From the Venetian "s'ciavo", "I am your servant". A friendly "Hi there" or "See you" in modern Italian.