In the Golden Empire, the Royal Holographic Network (shortened to Royal HoloNet in every medium but its own budget) was a means of instantaneous communication among the Empire's worlds and starships. It was maintained and expanded by the Ministry of Internal Affairs and Integration.
The explorers from the known galaxy who colonized the Vall`to Sector established a basic HoloNet, mimicking that of the Republic. However, the massive cost needed to maintain it, let alone expand it, led to this HoloNet falling into disuse, replaced by cheaper and slower subspace transmissions.
When the Vall`to Sector was conquered by the Tetrarchy of Mezlagob, the Tetrarchs acquired the HoloNet technology and revitalized the project, spending lavishly to keep all their worlds under tight control. However, this benefice extended only to the "main" worlds of the Tetrarchy; the "vassal" worlds usually still relied on the cheaper subspace transmissions.
The HoloNet truly took off, however, when the Tetrarchy itself went to war with the Golden Empire. Tariun Sakaros engineered a shadowfeed on the Tetrarchy's HoloNet, encouraging revolt on forcibly occupied worlds and spreading otherwise-suppressed news of the Empire's victories against the Tetrarchy. Famously, the Tetrarchy was embarrassed when it claimed the Battle of Tizgo V had been a victory, touting the death of the enemy general Keltrayu. Tariun retaliated by providing recordings of the actual battle which showed the Tetrarchy's forces being massacred, along with an accurate kill count.
When the Tetrarchy fell, Rin Sakaros incorporated the HoloNet (now renamed the Royal HoloNet) into her government, updating it with new technology from the known galaxy and expanding it to cover her entire Empire. Control and expansion of the Royal HoloNet was given to the newly-formed Ministry of Internal Affairs in 103 ABY.
The most common use of the HoloNet was to relay information among the member worlds of the Empire, both between systems and from the Royal government to all constituent worlds. Private citizens were encouraged to own HoloNet arrays, though they were expensive. Public HoloNet transceivers could be used for a nominal fee. Schoolchildren throughout the Empire had "HoloPals", children on other worlds with whom they could communicate via the Royal HoloNet.
The Glorious Armada of the Golden Empire used heavily encrypted HoloNet channels to relay military information.