Do Islam and Christianity have been influenced by Gnosticism?
Gnosticism is a religious movement consisting of various doctrines of the Mediterranean and the Middle East that are usually characterized by the belief that men are divine souls trapped in a material world created by an evil god or imperfect called the demure. The movement reached its peak during the second century.
Is that Gnosticism has influenced Islam and Christianity today?
I cannot answer about Islam, as I don't know particularly well.
Christianity has fought gnostic heresies since the second century. Gnostic heresies have made their reappearance periodically: for example, book "The Davin's Code" repackages and presents Gnostic viewpoints. That particular book recently had an enormous impact.
Christianity doesn't have many if any Gnostic influences remaining, the Catholic church saw to that. I doubt that Islam does either although Sufism the mystic side of Islam is similar to Gnosticism. Today it has more in common with Hinduism, Buddhism and Taoism.
The Demiurge as you probably know represents an aspect of humanity.