Fatcat
The Internet Archive's open catalog of scholarship — the editable backbone under IA Scholar.
Tier 3 Open AccessFree
Research Database Directory
Every research database, reviewed.
Research Rabbit
A free discovery engine that maps a field from the papers you already like.
Tier 2 ToolsFree
Inciteful
Fast, free citation-network analysis — find the papers that connect your papers.
Tier 3 ToolsFree
DOAB
The Directory of Open Access Books — DOAJ's counterpart for scholarly monographs.
Tier 3 Open AccessFree
OpenAIRE
Europe's open scholarly graph — publications, data, software, and funding, linked.
Tier 2 Open AccessFree
Unpaywall
The one-click route to a legal free version of almost any paper.
Tier 2 ToolsFree
Zenodo
CERN's catch-all repository — deposit any research output and get a DOI.
Tier 2 Open AccessFree
Open Science Framework (OSF)
The open-science workbench — manage a project, preregister, and share it all.
Tier 2 ToolsFree
WorldCat
The union catalog of the world's libraries — find who holds a book or item, and where.
Tier 2 ToolsFree
NASA ADS (Astrophysics Data System)
The free, comprehensive index for astronomy and physics — the field's shared memory.
Tier 2 Open AccessFree