Which Supermemory are you replacing?
Supermemory is two products in one. For developers it is a memory API and SDK. For everyone else it is a consumer second brain with a browser extension that captures context as you go. That makes "alternative" a fork in the road. If you used the API, the real alternatives are other memory backends: mem0 and Zep are the closest, both self-hostable. If you used it as a second brain, the alternative is a knowledge base you write in.
Captured for you vs written by you
Supermemory leans on capture: the extension and the API accumulate context automatically, and you read back what the engine kept. Hjarni asks for a deliberate act. You write the note, in plain Markdown, and that exact text is what ChatGPT and Claude read over the built-in MCP server. The trade is effort for control, and it pays off the day you need to know why your AI believes something: the answer is a note you can open, with a history of every edit and one-click revert.
Supermemory leans on capture. Hjarni leans on authorship.
Recall you can verify
For a memory product, the worst failure is a write that succeeds but never comes back. Supermemory users have reported documents visible in the app's own UI that returned nothing through API search, the MCP recall tool, or hybrid search. That risk lives in any recall pipeline you cannot see into. Hjarni's answer is architectural: notes are plain Markdown you can open and list, and one search index serves the UI, the REST API, and the MCP search tool. What you can see is what you can search.
When to stay on Supermemory
If automatic capture is the point for you, or you want the consumer app and the developer API in one product, Supermemory is a strong pick and the alternatives above will feel like a step sideways. It ships an official open-source MCP server, so it is not a walled garden. Check their current pricing across the developer and consumer tracks, and note the hosting: Supermemory is US-based, while Hjarni runs in the EU (Germany).