CyberWriter is a Markdown editor built on Apple's on-device AI stack — Foundation Models (macOS 26), NLContextualEmbedding, and SFSpeechRecognizer — so your notes never leave your machine. It indexes your entire Markdown vault locally using a BERT-style 512-dim embedder, then surfaces semantically related notes in search results even when the exact words don't match. Ask a question in the search bar and it retrieves the top five relevant chunks as context for a local RAG chat — no API key, no cloud call, no per-token cost. For writing, Command+Shift+A opens a full chat panel and Command+J triggers inline actions: rewrite, summarize, change tone, fix grammar, or continue. Apple Intelligence is the default model, but Claude, OpenAI, Ollama, and LM Studio all slot in if you prefer. Built specifically for users who handle sensitive content — health data, private research, confidential notes — and need AI assistance without handing files to a third-party service.