Sidelong is a writing app that comes built with your entire knowledge library attached. You save anything you read, watch, or listen to: articles, YouTube videos, podcasts, tweets, Kindle highlights, newsletters, etc. It summarizes everything, pulls out the key points, and makes it searchable. Then, while you type, it surfaces anything relevant to what you re writing, while you re writing. There s also a chat that answers from what you ve saved.It doesn t write for you. You can ask it to research something or to tear a draft apart, but it won t produce prose. I think AI-written blog and newsletter posts are still pretty bad and didn t want to make a machine for more of them.When a piece is done you can export to Substack or Beehiiv, publish to a hosted blog it gives you, send it as a newsletter, or post it directly to X and LinkedIn as a thread.Gaps: the Chrome extension is still in store review as I write this, no mobile app, not local-first. Feedback I d use: whether the retrieval feels good, and what you save from that it doesn t handle yet.