Obsidian is a free Markdown editor for Linux, MacOS and Windows. You can use Obsidian as note taking and Knowledge Base application. It is free for personal use and no signup required. All data are stored in your local system in plain text Markdown files. But you can sync that files with Dropbox. You can extend its feature with plugins. It supports Git versioning, Internal link, Graph view, Audio recorder, LaTeX math, Slides, Backlinks and word counts. It is still in beta stage and active development.