The Khitan scripts were the writing systems for the now-extinct Khitan language, used in the 10th-12th century by the Khitan people. who had created the Liao Empire in north-eastern China. There were two scripts, known as the large script and the small script. These were functionally independent and appear to have been used simultaneously. The Khitan scripts continued to be in use to some extent by the Jurchens for several decades after the fall of the Liao Dynasty, until the Jurchens fully switched to a script of their own. Examples of the scripts appeared most often on epitaphs and monuments, although other fragments sometimes surface.
More information on the Wikipedia page [1]. The Ancient Scripts page is [2] and the Omniglot page [3].