From their “About” page:
“Intute is a free online service providing access to the very best web resources for education and research. All material is evaluated and selected by a network of subject specialists to create the Intute database.
The Intute database makes it possible to discover the best and most relevant resources in one easily accessible place. You can explore and discover trusted information, assured that it has been evaluated by specialists for its quality and relevance.”
They have organized the pages by very broad subject areas: Health & Life Sciences, Arts & Humanities, Social Sciences and Science Engineering & Technology Environment has recently gained separate category status: Intute Environment Gateway