What’s a simple FOSS journaling and logbook app for Linux Mint?

SilverBullet may fit if you like the idea of a lightweight, browser-based notebook. It uses Markdown-style notes and links, can be self-hosted locally, and uses relatively little RAM. For a strictly desktop FOSS setup, Logseq is also worth considering; it is open source and focuses on linked, journal-style entries. Both are better matches for your requirements than closed-source note apps.

Zim Wiki is worth a look. It stores your notes as plain text files in a hierarchical notebook, so you can organize entries by date, topic, or both. It supports links, tags, searching, and optional Markdown-like formatting without feeling overly complicated. It’s been reliable for long-term notes and is lightweight enough for your hardware.

You could skip a dedicated notes app and use a Markdown-capable text editor with folders of plain text files. Keeping the folder in a Git repository gives you history and backups, while Markdown keeps everything readable in the future. This is probably the lowest-resource and most portable approach, especially for system logs and troubleshooting notes.

Trilium is another good option if you want a more structured notebook. It’s free and open source, supports nested notes, and is still fairly straightforward for keeping technical logs or personal records. It’s more like a full notes database than a basic text editor, but it doesn’t require a complicated workflow.