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), allows I/O in 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 dialect* "s'ciavo", "I am your servant". A friendly "Hi there" or "See you" in modern Italian.