Personal Knowledge Management (PKM) has shifted from a niche productivity hobby to a serious discipline embraced by developers, researchers, students, and founders. On Reddit, communities like r/ObsidianMD, r/PKMS, and r/NoteTaking are filled with in-depth workflows for building a “second brain” — a trusted external system that stores, connects, and retrieves ideas across PDFs, podcasts, highlights, and daily notes. The goal is not hoarding information, but turning scattered data into structured, searchable insight.
TL;DR: Reddit power users consistently recommend a small set of PKM tools for building a second brain: Obsidian, Logseq, Notion, Readwise + Reader, Recall, NotebookLM, Devonthink, Capacities, and Roam Research. These tools excel at importing PDFs, transcribing podcasts, linking atomic notes, and enabling long-term retrieval. The strongest systems combine knowledge capture with intelligent summarization and spaced repetition. Choosing the right stack depends on whether you prioritize local control, AI assistance, or collaboration.
Contents
What Makes a Strong Second Brain Tool?
Before diving into the top nine tools, it’s important to understand what Reddit “geeks” typically look for in a PKM system:
- Bidirectional linking between ideas
- Markdown or open format storage
- Strong PDF handling with highlights and annotations
- Podcast or audio transcription support
- Search and recall capabilities, ideally AI-assisted
- Longevity and export options
The following tools meet these criteria in different ways.
1. Obsidian
Obsidian remains the dominant choice among Reddit PKM enthusiasts. It stores notes as local Markdown files, giving users full ownership and long-term stability. Its signature feature is bidirectional linking, allowing ideas to form a network rather than isolated pages.
Why Reddit loves it:
- Massive plugin ecosystem
- Graph view visualization
- Advanced PDF annotation plugins
- Integration with Readwise and Omnivore alternatives
Many users import PDF highlights directly into Obsidian and connect them to permanent notes using a Zettelkasten-inspired workflow. With plugins, you can even transcribe podcasts and store summaries alongside linked insights.
Best for: Users who want full control, flexibility, and long-term reliability.
2. Logseq
Logseq is often described as “outline-first Obsidian.” It combines local Markdown storage with block-based referencing similar to Roam Research.
Reddit users value Logseq for:
- Daily journal-driven knowledge capture
- Block-level linking and embedding
- Built-in spaced repetition flashcards
- Strong PDF annotation tools
If your learning system revolves around revisiting ideas regularly, Logseq’s integrated flashcard features make it especially appealing.
Best for: Learners who want built-in spaced repetition inside their PKM.
3. Notion
Although not as “hardcore” as Obsidian in Reddit circles, Notion remains extremely popular due to its elegant interface and database capabilities.
Strengths include:
- Structured databases for research tracking
- Embedded PDFs and media
- Collaboration and team sharing
- Clean UI
The downside frequently mentioned on Reddit is vendor lock-in and limited offline functionality. Still, for collaborative second brains or startup knowledge hubs, Notion is difficult to ignore.
Best for: Teams or individuals who prefer structure over raw flexibility.
4. Readwise + Reader
Readwise is less of a note-taking app and more of a knowledge ingestion engine. It syncs highlights from Kindle, Instapaper, Pocket, and more. Its companion app, Reader, allows PDF and web article annotation.
Why it fits a second brain:
- Automatic highlight syncing
- Daily email resurfacing old insights
- Easy export to Obsidian, Logseq, or Notion
- Podcast transcript highlighting
On Reddit, many users treat Readwise as the “capture layer” and Obsidian as the “thinking layer.”
Best for: Avid readers and podcast consumers.
5. Recall
Recall is gaining serious traction among Reddit productivity communities because it focuses on one essential challenge: remembering what you consume.
Recall allows users to:
- Summarize YouTube videos and articles automatically
- Generate structured knowledge cards
- Review insights using spaced repetition
- Create knowledge graphs automatically
Its AI-assisted summarization reduces friction between intake and understanding. For people overwhelmed by high-content platforms like YouTube and podcasts, Recall functions as a cognitive filter.
Best for: Users who prefer AI-summarized learning integrated with revision.
6. NotebookLM
NotebookLM (by Google) takes a different approach: instead of being a traditional PKM tool, it acts as an AI research companion grounded in your own uploaded documents.
Core strengths:
- Upload PDFs and ask contextual questions
- AI-generated summaries grounded in your sources
- Source citation linking
- Ideal for academic research
Reddit researchers highlight NotebookLM as particularly powerful for thesis work, literature reviews, and complex document analysis. However, it is not yet a complete second brain on its own — it complements other storage-focused systems.
Best for: Deep document analysis and academic workflows.
7. Devonthink
Devonthink is a veteran tool, especially popular among Mac users. It emphasizes intelligent document management rather than pure note linking.
Notable capabilities:
- AI-assisted document classification
- Robust PDF storage and OCR
- Email archiving
- Advanced search operators
Some Reddit users use Devonthink as a secure archive layer combined with Obsidian as their idea-connection layer. It shines when managing thousands of research files.
Best for: Professionals with large document libraries.
8. Capacities
Capacities introduces an object-based note-taking approach. Instead of only pages and backlinks, it lets users create structured “objects” (people, books, topics) and connect them semantically.
Praised features:
- Modern and intuitive design
- Visual graph exploration
- Media-friendly notes
- Structured knowledge modeling
Reddit users often recommend Capacities to beginners intimidated by Obsidian’s plugin culture but still wanting networked thinking.
Best for: Visual thinkers and structured creatives.
9. Roam Research
Roam Research popularized the modern bidirectional-linking renaissance. While its growth has slowed, many Reddit veterans still swear by it.
Advantages:
- Frictionless block referencing
- Daily note-centric workflow
- Strong community templates
Criticism typically centers around pricing and offline limitations. Still, its influence on the PKM ecosystem is undeniable.
Best for: Pure networked thought with minimal setup.
How Reddit Users Combine These Tools
Interestingly, most advanced users do not rely on one tool alone. Common “second brain stacks” include:
- Readwise + Obsidian for capture and deep linking
- Recall + Logseq for AI summaries plus spaced repetition
- Devonthink + Obsidian for archival and conceptual thinking
- NotebookLM + Notion for research-heavy projects
This layered approach mirrors how the brain functions: capture, process, connect, retrieve.
Final Considerations
Building a second brain is less about the tool and more about consistency. Reddit discussions repeatedly emphasize:
- Create atomic notes (one idea per note)
- Link aggressively
- Review regularly
- Avoid over-optimizing your system
Tools like Recall and NotebookLM are accelerating AI-assisted comprehension. Meanwhile, platforms like Obsidian and Logseq preserve durability and data ownership. The strongest approach blends intelligent summarization with permanent, linked storage.
In the end, the best PKM tool is the one you trust enough to use for years. A second brain is not built in a weekend — it evolves into a long-term thinking infrastructure.
If there is one lesson repeated across Reddit’s most experienced knowledge builders, it is this: Capture what matters. Connect it deliberately. Review it often. The tools above simply make that discipline scalable.
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