Obsidian is a local-first Markdown note-taking app developed by a Canadian team. The core app is free and it is known for bidirectional links and the knowledge graph. With 1000+ community plugins and paid Sync/Publish add-ons, it is a popular choice for personal knowledge management and a second brain.
WorkFlowy is an infinite-level outliner released in 2010 by a US team, known for Zoom focus and minimalist text. The free plan offers limited nodes and Pro costs about $4.99-9.99 per month, making it a pioneer of outline-based thinking.
RemNote is a notes-plus-memory tool for students that deeply combines note-taking with spaced-repetition flashcards, supporting PDF annotation, bidirectional links, and multi-platform sync, free tier available and Pro about $8/month.
Reflect is an AI-powered, end-to-end encrypted notes app combining Daily Notes, bidirectional links, and built-in AI summaries and Q&A at about $10/month, an Obsidian-style choice for privacy-conscious users.
Foam is a free, open-source personal knowledge management tool built on VS Code, using local Markdown files and bidirectional links to build a knowledge graph, completely free under the MIT license, suited to technical users familiar with VS Code and Git.
Roam Research is a personal knowledge management tool from San Francisco, founded in 2018, that pioneered block references and bidirectional links. Built around Daily Notes, outlining and a graph view, it costs about $15 per month and defines the "Roam-like" PKM paradigm.
Logseq is an open-source local-first note-taking app launched in 2021 by a US team, built around outlining and bidirectional links; notes are stored as Markdown files locally with PDF annotation and whiteboard support, a popular choice for building personal knowledge bases.