The Ixians were a society that specialized in the production of complex machinery that often flouted the proscriptions of the Butlerian Jihad which led to a near-taboo on the creation of machines in the image of the human mind. Its name was derived from the their home planet that was the ninth of Alkalurops.
The Ixians were ruled by House Vernius. Emperor Elrood IX, who desired a Melange substitute and who wanted to pay back Dominic Vernius for two offenses against him (stealing a concubine - later to be called Shando Vernius from Elrood and making larger Heighliner ships, stripping Elrood of tax revenue), decided that a Tleilaxu invasion of Ix would kill two birds with one stone.
The Tleilaxu invade in Dune: House Atreides, on the (somewhat justified) pretext that House Vernius were creating thinking machines (a fighting Mek was created shortly before in the story) and are driven out of Ix in House Corrino. Some years later the Ixians are freed from the Tleilaxu.
By the time of Dune the Ixians are, other than the Bene Tleilax, probably the most successful of the fringe worlds that maintain a sophisticated technological base, having had their technological base rebuilt at the cost of House Corrino reparations. Their form of government seems to have been transformed into a meritocracy or perhaps Technocracy.
During the Famine times the Ixians became a major power in the known universe, with the invention first of no-ships which contain machines that duplicate the abilities of Guild Navigator, hide the people within from prescience; with the advantage of being far cheaper. It is the development of this cheaper form of space travel which fuels the Scattering.
By the time of Heretics of Dune the power of the Ixians seems at its apex with their alliance with the Fish Speakers; but Bene Gesserit analysts see them as a failing power, because Ixian society has become a bureaucracy and no great inventions have come out of the workshops of Ix for centuries.
When the Honoured Matres conquer the Old Empire, the Ixians are reduced to being a barely tolerated technological combine.
Ixian Technology in The Dune Games
The Ixians are responsible for providing the technologies for the three Houses to build their unique tanks. This is done by building the Ixian Research Facility at the player's base. Once this is done, the player will be able to build either the Atreides Sonic Tank, the Harkonnen Devastator, or the Ordos Deviator. Other than that, they serve no other purpose.
Emperor: Battle For Dune
In the War of Assassins, the Ixians now play a more direct role in combat, interacting with the three Houses as trading partners. An alliance with House Ix can be forged by aiding them in various missions, providing that the player doesn't ally with the Tlielaxu first, as the two are bitter enemies.
Once allied, the Ixians will provide the player with units built from the House of Ix. These include the Infiltrator (a stealthed mobile kamikaze unit that reveals cloaked enemy units when it detonates), and the Projector Tank (fast hover tank with light mounted cannon, which when deployed, is able to project holographic images of the player's troops that provides realistic damage, yet disintergrates harmlessly on impact).