https://www.humantruth.info/tags/gnosis.html
Human Truth Foundation pages (4):
A List of Christian Denominations and Sects
Gnosticism (1st-7th Century): The Birth of Christianity
Historical Christianity: Who Were the First Christians?: 2.6. Gnosticism (1st-7th Century)
St Paul - History, Biblical Epistles, Gnosticism and Mithraism: 5. Gnosticism
Not from the Human Truth Foundation, but still relevant (2):