Trilium Notes is a free and open-source, cross-platform hierarchical note-taking application focused on building large personal knowledge bases. Notes can be arranged into an arbitrarily deep tree, and a single note can be placed in several places in it. Trilium runs as a desktop application on Windows, macOS and Linux, or on a self-hosted server, including via Docker, that syncs notes across devices and can be reached from a web browser, including on mobile.
As of November 2026, the project is maintained by the TriliumNext community: its README says the original Trilium developer has given the Trilium repository to the community project. The README lists a rich WYSIWYG editor with tables, images, math and 📝Markdown autoformatting, strong note encryption with per-note granularity, scripting, relation maps and note/link maps for visualizing notes and their relations, a web clipper for saving web content, and synchronization with a self-hosted sync server. The project's site describes Trilium as programmable, says a note marked as encrypted is encrypted using AES-128-CBC, and states that its AI features are opt-in and disabled by default. The site also says there is no official mobile application. The code is licensed under the GNU Affero General Public License v3.