Lampyre - Lampyre - an efficient data analysis and OSINT multi-tool for everyone.
Dia - Dia is a GTK+ based diagram creation program for GNU/Linux, MacOS X, Unix, and Windows, and is released under the GPL license.
DataWalk - DataWalk is a software platform to connect numerous large data sets, both external and internal, into a single repository for fast visual analysis.
draw.io - Online diagramming application
Sentinel Visualizer - Link Analysis, Data Visualization, Geospatial Mapping, and Social Network Analysis (SNA) with Sentinel Visualizer
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.