The Kane Chronicles

The Kane Chronicles is a book series written by Rick Riordan. It is hinted that it exists in the same universe as Percy Jackson and the Olympians and The Heroes of Olympus.

Relationship with Percy Jackson and the Olympians
The series makes occasional references to the Percy Jackson and the Olympians series, as it takes place in the same world.
 * Towards the beginning of the book Amos states that Manhattan has its own set of gods and that they must be kept separate from Egyptian gods. He says this while looking at the Empire State Building, the current home of Mount Olympus.
 * When the Egyptian goddess Bast needed a portal she said that "I try to avoid Manhattan, but this is an emergency". She presumably wanted to avoid Manhattan because she knew that Olympus is there.
 * Later in the book, Thoth mentions that the Greeks confuse him with Hermes, something he takes offense to as Hermes is apparently of a very different person.
 * In the second book, The Throne of Fire, Carter catches a glimpse of a winged horse flying around Manhattan, and recalls what Amos said about Manhattan and its gods.
 * Nico travels to a New Orleans graveyard, Anubis is fond of New Orleans and the Hall of Judgement is connected to a graveyard while Anubis is in charge of it.
 * In Throne of Fire, Sadie met several Roman mummies who used the Di immortals swear and mentioned Pluto, Jupiter, and Vulcan. Later, the God Ptah mentioned that they went on to 'whatever afterlife they were destined for' referring to the Underworld.
 * In flashbacks, Bes was shown fighting demons during World War II, a conflict started by demigod sons of the Big Three, as well as dressed in a Roman toga with Tarawet.
 * Drew and Lacy appear as Sadie's schoolmates in America, mentioning they go to the same summer camp during the Serpents Shadow. They are later mentioned to go to some sort of camp, which is presumably Camp Half-Blood.
 * Later, the book references bursts of magic from Long Island.
 * The Williamsburg Bridge appears in both series.
 * Nico looks like Anubis.