The closest category overlap of the bunch
Of the developer-memory tools, Supermemory is the one that lands nearest to Hjarni, because it is two things at once: a memory API and SDK for developers, and a consumer second brain app with a browser extension. So part of Supermemory really does compete with a notes app. The honest difference is in posture. Supermemory leans toward AI capturing memory for you, often automatically, with the API first. Hjarni leans toward a person writing Markdown notes that AI then reads.
Both ship an MCP server. Supermemory's is official and open-source, with read and write and OAuth or API-key auth, and works with Claude Desktop, Cursor, and VS Code. Hjarni's is built into the knowledge base. Both are model-agnostic.
Captured for you vs written by you
The browser extension is a good tell. Supermemory wants to capture what you read and turn it into recallable context with little effort. That is genuinely useful when you want memory to accumulate in the background.
Hjarni asks for a deliberate act: you write the note. The upside is that what your AI reads is exactly what you decided to write, in plain Markdown you own and can export as a ZIP at any time. The trade is effort for control.
Supermemory leans on capture. Hjarni leans on authorship.
When Supermemory is the better fit
If you want one product that is both a personal-memory app and a developer memory API, and automatic capture appeals to you, Supermemory is a strong pick. If you are also building on top of a memory API, having the consumer app and the developer surface in one place is convenient. Check their current pricing across the developer and consumer tracks before you commit.
When people choose Hjarni instead
Two reasons come up most. First, EU hosting: Hjarni runs in Germany, while Supermemory is US-based. Second, the Markdown-file knowledge base: people who want notes they author and own, with folder-level AI instructions, tend to prefer writing to reading back what a tool captured. If your source of truth is a note you write, Hjarni fits. If it is context an engine gathers, Supermemory fits.