VOSviewer
Free software for mapping bibliometric networks.
Tier 2 ToolsFree
Research Database Directory
Every research database, reviewed.
WorldCat
The union catalog of the world's libraries — find who holds a book or item, and where.
Tier 2 ToolsFree
zbMATH Open
The free, open index of the mathematical literature.
Tier 2 Open AccessFree
Zenodo
CERN's catch-all repository for any research output.
Tier 2 Open AccessFree
Zotero
The free, open-source reference manager most researchers already have — and underuse.
Tier 2 ToolsFree
ROR
A persistent ID for every research organization — ORCID for institutions.
Tier 3 ToolsFree
Érudit
Canada's open platform for French-language scholarship.
Tier 3 RegionalFree
SciELO
Latin America's open-access flagship — the network the big commercial indexes under-count.
Tier 2 RegionalFree
Sciety
The fastest way to see whether a preprint has had expert eyes on it.
Tier 3 ToolsFree
Scilit
A fast, free scholarly index — MDPI's comprehensive metadata search.
Tier 3 Open AccessFree