Heptabase is a freemium knowledge management platform built around a visual, whiteboard-first architecture. It features a block-based editor with bi-directional linking, multi-model AI agent support (GPT, Claude, and Gemini), and a CLI agent interface compatible with Claude Code and Codex. The platform exposes an API and integrates with external tools including Readwise, Zotero, PDF annotation pipelines, YouTube transcript ingestion, and a Web Clipper. AI credits are consumed per model interaction; credit allocations vary by tier (100/mo on Pro, 1,800/mo on Premium, 8,100/mo on Premium+). GitHub activity sits at 154 stars.