InfraNodus - Generates research insights using text network visualization and analysis.
LucidChart - LucidChart is the missing link in online productivity suites. LucidChart allows users to create, collaborate on, and publish attractive flowcharts and other diagrams from a web browser.
arXiv - arXiv is a free distribution service and an open-access archive for scholarly articles.
draw.io - Online diagramming application
Unpaywall - Legally read research papers behind paywalls.
yEd - yEd is a free desktop application to quickly create, import, edit, and automatically arrange diagrams. It runs on Windows, Mac OS X, and Unix/Linux.