Using citations, Inciteful looks for links between academic literature. They’re committed to being free and open access.
Key features:
No need to login. Inciteful has two options to start exploring the literature:
Paper Discovery – use a seed paper to build a network of literature from the citations.
Library Connector – cross disciplinary searching using two papers.
Limitations:
You can get lost adding papers and lose track of where you were and what you want.