The Thinking Machines are machines in an empire controlled by the computer evermind known as Omnius. They were first created by the old Empire to do everyday tasks for humans. The old empire was overthrown by the Twenty Titans who used these machines to conquer it. During the time of the Butleruan Jihad most thinking machines were controlled by Omnius with a few exceptions. The only notable ones of these exceptions are Erasmus, who killed Serena Butler's infant son while she was his slave, and Seurat, Vorian Atredies' machine partner during the time he served in the Omnius Empire.
The cymeks were part of the omnius empire but were not thinking machines. They were cruel people who had their brains put into canisters that could be used to control various machine bodies. The only notable cymeks are the Titans Taloc, Agammemnon, Juno, Hectae, Ajax, Barbossa, and Xerxes.