Skimming through their Wiki, it looks like a tree-oriented outliner with a link graph - i.e. a similar model to what Roam, Obsidian, Logseq or org-mode (especially when paired with org-roam) offers.
This is as close as I've seen graphs at the UI level to hit mainstream, and the extreme hype generated around this class of tools (and Zettelkasten) when Roam showed up was interesting to watch - people reacted to this as if it was pure magic.
It's a generic note storage (with a DAG based model) that's very extensible and comes with a demo task manager implementation: https://github.com/zadam/trilium/wiki/Task-manager