Yes, I use my own topics map-based solution, Contextualise: https://brettkromkamp.com/projects/contextualise/. In simple terms, you create topics, attach resources (e.g., PDFs, markdown text and notes, images, etc.) to those topics and establish semantically meaningful relationships between the topics. The resulting map of topics can be navigated by means of a visual network graph. Contextualise is a MIT-licensed open source project.