What are some alternatives?
draw.io - Online diagramming application
Linkurious - Search and visualize your graph data through a simple web-based interface
PlantUML - PlantUML is an open-source tool that uses simple textual descriptions to draw UML diagrams.
Gephi - Gephi is an open-source software for visualizing and analyzing large networks graphs.
Dia - Dia is a GTK+ based diagram creation program for GNU/Linux, MacOS X, Unix, and Windows, and is released under the GPL license.
Cytoscape - Cytoscape Official Web Site