Semantic Scholar is a free research search engine from the Allen Institute for AI (Ai2), a nonprofit in Seattle. It launched in 2015.
It indexes a very large number of scientific papers across all fields. AI generated TLDR summaries give the main point of a paper in one sentence. Citation graphs show which papers influenced a work and which built on it, and highly influential citations are flagged. The Semantic Reader explains citations and terms in context while reading. Research feeds suggest new papers based on a user's library.
Semantic Scholar is free, and its data is available through a public API.