Palladio is a project of Stanford's Humanities + Design Research Lab. The web-based application is free to use. You are able to import your tabular data into Palladio and visualize it in a map, graph, table, or gallery view. You can change the size of the dots (nodes) for each visualization to correlate with the frequency with which they appear in your dataset. Your Palladio project is exportable and you can revisit it at a later time within the platform.
Project using Palladio: Andrew W. Wilson, Mapping the Revolution (2016)
Gephi is a free and open source visualization software for graphs and networks. Gephi can be used for exploratory data, link, social network, and biological network analyses. Users can create real-time visualizations with networks of up to 100,000 nodes and 1,000,000 edges. You can add to the functionality of the software by installing plugins. Gephi is notoriously buggy and has not been updated in several years but is still useful software for network analysis.
Project using Gephi: Gönül Aycı, A Simple Project With Gephi (2017)