draw.io - Online diagramming application
UCINET - UCINET for Windows is a software package for the analysis of social network data.
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.
Gephi - Gephi is an open-source software for visualizing and analyzing large networks graphs.
PlantUML - PlantUML is an open-source tool that uses simple textual descriptions to draw UML diagrams.
Pajek - Pajek is a lightweight solution developed from scratch by an extraordinary team of developers for the purpose of Large Network Analysis.