SumizAI vs ExtMemo

What ExtMemo is

ExtMemo is a Chinese notepad app with end-to-end encryption (E2EE) and AI assistance, described by its creators as "the premier external memory system for high-value thinkers" — an ambitious tagline, but one reflecting a real feature set: logical note chains, E2EE-level privacy, and secure team sharing with no loss of that privacy.

The key feature is "logical chains" — a way of organizing notes into connected sequences of thought, where each subsequent note builds on the previous one in a more structured way than plain wiki-linking. Team members can edit together within the same chain, with conflict-free collaboration — each person modifies their own nodes with no sync conflicts with others.

A "Privacy-First AI Guardian" organizes note threads without peeking at the actual ai notes content — an unusual approach to integrating AI with a notepad: instead of sending raw content to a language model for categorization, ExtMemo claims a mechanism that allows organization without exposing content, addressing the typical conflict between AI feature convenience and full privacy of encrypted data.

The "Nebula View" feature offers 3D visualization of notes — ExtMemo computes semantic vectors of content and builds an interactive "galaxy" where thematically related notes naturally cluster and orbit each other within the user's knowledge base. That's one of the more unusual, visually striking features among all the ai notes tools in this list.

The pricing model — a subscription in the $2-3/month range plus a feature-limited free version — is one of the cheaper options on the market among apps offering full E2EE encryption and AI features at once, making ExtMemo affordable even for individual users, not just companies.

Availability across multiple platforms (web, iPhone, iPad, Firefox as SaaS) with no Android or Windows/Mac desktop version limits usefulness for some potential users — a typical limitation of younger products prioritizing the Apple ecosystem and the web over full coverage of every platform.

For professionals working with sensitive client data (lawyers, consultants, therapists) needing both encryption and team collaboration, ExtMemo offers a rare combination of both requirements — most competing ai notes tools offer either full E2EE with no team collaboration, or collaboration with no full end-to-end encryption.

Compared to simpler, unencrypted AI notepads, ExtMemo requires greater trust in the encryption implementation itself — for the average user, it's hard to verify whether the claimed E2EE is actually implemented correctly without an independent security audit of the code by outside experts.

For researchers and consultants who need to show clients their notes and findings are handled with the utmost confidentiality, the "E2EE encryption" label itself can be a selling point — it's easier to convince a demanding client to entrust sensitive information when the tool's vendor openly states that even they have no access to the ai notes content stored in the system.

It's also worth noting that the Chinese origin can raise additional questions about legal jurisdiction and potential government access to data, regardless of the claimed encryption — for some Western organizations, especially in regulated sectors, that's a more decisive factor than the notepad app's technical features themselves.

In short, ExtMemo is an ambitious, cheap notepad app with E2EE encryption, logical thought chains, and striking 3D visualization — a solid option for people wanting to combine privacy with AI capabilities in one note-taking system, though platform-limited to the Apple ecosystem and the web.

What SumizAI is

A note-taking application built around a conversation with an AI model. You ask a question, the answer streams back, and the answers worth keeping become Markdown notes — filed into a vault that is a folder on your own disk.

A vault is a directory holding base.md, a generated table of contents up to six levels deep, and a notes/ folder with one .md file per note. Before a note is written it is checked against the ones already there, so the fourth note about the same idea gets merged instead of added. Links between notes are ordinary Markdown links to files that exist.

The model is never ours: you bring your own API key to one of seven providers — Anthropic, OpenAI, Gemini, Groq, OpenRouter, a local Ollama or your own server — and pay that provider directly. A question sends the table of contents plus at most five relevant notes within a 24,000-character budget, and the app shows you which five it used.

Every answer kept this way becomes one of these ai notes, ready to search again months later without hunting back through old chats.

Side by side

Where they differ

• Both mention AI. The difference is whose key it runs on: SumizAI never resells inference — you connect one of seven providers (Anthropic, OpenAI, Gemini, Groq, OpenRouter, a local Ollama or your own server) with your own API key and pay that provider directly. Check what ExtMemo does with the model bill before comparing prices.
• ExtMemo is freemium: there is a free tier and a paid one, and the line between them is the thing to read before committing. SumizAI has one plan at a dollar a month, so there is no feature held back for a higher tier — and an unpaid account still opens and exports every vault it already has.
• AlternativeTo's description of ExtMemo does not mention Markdown, so check what format your notes end up in before you fill it up. SumizAI writes standard .md files to a folder you picked, and an unpaid account can still export all of them.
• ExtMemo is described as something more than one person uses at once. SumizAI is not: there are no shared vaults, no comments, no permissions and no sync between devices. If the work is a team's, that is a reason to pick ExtMemo over SumizAI.
• ExtMemo runs in the browser. SumizAI is a desktop and mobile application, and on the desktop the vault is a folder on your own disk rather than a document in someone's cloud.

Which one to pick