Ego Stone : 7th Infinity stone in Marvel universe.

Infinity War explains the Infinity Stones were created by the Big Bang that gave birth to the universe. In the comics, there are seventh infinity stones Space, Mind, Soul, Time, reality, power and Ego stones. The seventh Gem was hidden in an unknown realm known as the Ultraverse. The first appearance of Ego stone in July 1995 in Avengers vs Ultraforce crossover comic. This goldish color gem was said to obtain the essence of Nemesis. She was the omnipotent being, which shattered herself across two universes, because she grown tired of her own existence.
The comics do not explain the Ego Stone’s power in great detail, saying only that it’s very powerful and that there was a time it took possession of a former Avenger named Sersi. When the Ego Stone comes into contact with the other Infinity Stones, Nemesis will be reborn.

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There are two more stones which are not  appeared in  marvel universe/comics but appeared in Marvel video games and animated movie.

Rhythm(pink color)
In the Marvel Super Hero Squad universe and related media, a seventh Rhythm Gem exists. The acquisition of the Infinity Gems is the main focus of The Super Hero Squad Show's second season as well as the Marvel Super Hero Squad: The Infinity Gauntlet video game. The Rhythm Gem is revealed to be a fake Gem created by Loki as part of a scheme.

Build(red color)
In the Lego Marvel Super Heroes - Guardians of the Galaxy: The Thanos Threat animated film, a seventh Build Stone exists. Thanos seeks to possess the Build Stone in order to build a weapon.