Pantaphon

The Pantaphon (also called the Lygadi Deae) is a massive, ancient device, apparently designed to facilitate communication over vast distances. Located at the heart of the city of Nairida, on what is now Zak'kon, its origins are unknown, and may predate even the Protheans.

Description
In the simplest terms, the Pantaphon is a map portraying the telecommunication infrastructure for every explored system in the galaxy. By looking at it, one could theoretically discern the location and frequency of any piece of telecommunications equipment. But those are the simplest terms; the Pantaphon is exponentially more complicated.

Before she was overthrown, Meddianta T'Nair grew increasingly paranoid about the possibility of her colleagues using the device. In order to prevent that eventuality, she somehow managed to completely overhaul the Pantaphon's interface. According to the few salarians who managed to see the inside of the Pantaphon chamber before T'Nair banished them, the interface originally showed an accurate map of the galaxy, albeit one that was several centuries out of date. When Meddianta was overthrown by her daughter Eumenia, she found that the interface was drastically different. As she noted with considerable horror in her personal journal, the planets, stars, and systems that previously populated the map had all been replaced by elaborately-rendered avatars from Ancient Imerian mythology, ranging from entire legions of cherubs to two massive goddesses, locked in coital embrace. "Clearly," Eumenia wrote, "my mother's brilliant mind was lost, and with it, any hope of continuing her work."

In 2181 CE, it was rumored that Eumenia's daughter, Siani, managed to crack her grandmother's code, but this remains unconfirmed; Siani has stated that she believes the galaxy is better off not trying to comprehend the Pantaphon, and thus is disinclined to publish her findings.

Trivia

 * Pantaphon comes from the Greek panta (all) and foni (voice). Its Imerian name, Lygadi Deae, is a bastardization of llygad y dduwies, which means "Eye of the Goddess" in Welsh, with the dduwies replaced by the Latin word for "goddess", deae (to be closer proper asari, it should probably have been the Greek theas, but the author preferred deae because it fits better with the bastardized Welsh.)