Short answers, pulled from the story.
Greg Stafford created the fantasy world Glorantha in 1966 while he was a college student at Beloit College. He began developing the setting as a personal intellectual exercise to understand the nature of myth rather than to sell a product.
The world Glorantha is flat with a dome-like sky that has been shaped by the mythic actions of the gods during the Godtime. The continents of Genertela and Pamaltela exist within this structure where the gods are active participants in reality rather than distant figures.
The Mostali are stone-dwelling miners who are literally made of stone and invented iron which has extraordinary magical properties. The Aldryami are intelligent mobile plants who worship nature and the sun and are physically alien to what they call meat men.
The central conflict of Glorantha is a complex geopolitical and mythological war between the Storm God Orlanth and the Lunar Empire led by the imperial Sun God and the devious Moon Goddess. This struggle plays out across the northern continent of Genertela and defines the history of the setting.
The first game set in Glorantha was White Bear and Red Moon which arrived in 1975. It did not name the world it inhabited and instead hid its true identity behind a map of Dragon Pass and a story of constant war between Sartar and the Lunar Empire.
The Glorantha community has produced numerous media including magazines like Tales of the Reaching Moon and video games such as King of Dragon Pass released in 1999. Fan creations and unofficial business ventures like Reaching Moon Megacorp have kept the setting vibrant even during periods of corporate uncertainty.