SigmaNote

SigmaNote is an AI-powered second brain for students and knowledge workers who need one place to capture, organize, and query knowledge across formats.

Key capabilities include:

• Multi-format capture and importing from PDFs (text or image based), EPUBs, Office files, web articles, and YouTube links with auto-transcripts, plus sharing files from iOS apps.
• Chat with your knowledge using AI agents grounded in your data, with conversation-based Q&A that can reference multiple sources.
• Voice notes and transcription via real-time audio recording that converts speech into searchable transcripts.
• Knowledge-to-output creation to generate editable summaries, reports, articles, and notes, supported by natural-language search and an organized knowledge tree.

Pricing: Freemium. Free tier ($0) includes 5 knowledge imports/day, 5 AI prompts/day, and 5MB max file size; Premium is $8.99/month or $81.99/year.

What makes it notable: It combines grounded AI chat, cross-format importing, and end-to-end encrypted storage, designed for learning and writing workflows across web and iOS.