Logseq https://github.com/logseq/logseq is also a good OSS alternative and they're also working on collaborative feature I believe.

Obsidian (https://obsidian.md) also offers offline, + for free.

Are either Roam or Obsidian collaborative?

Not sure about Roam, I've been using Obsidian, and my purpose is for personal, making note archive offline. So never had any need for collaboration. But with Sync and Publish features, maybe there is a possibility.

Roam seems to be working on it. I’m unsure the status as I haven’t checked in a few months.

I think Roam has been fully collaborative since the launch. The browser keeps the whole database in IndexedDB and syncs it continuously with a WebSocket streaming Datomic-style transactions.

Roam: yes Obsidian: unsure (I think not)

Zero cost but not Free Software. Another untrustworthy thing like Notion.

I'm most saddened by the people who spend their time writing plugins for Notion / Roam (and to a lesser degree, Obsidian), providing extra value for free to a non-free product that will profit off the free labor. (or rather, I'm saddened that companies like Roam are so willing to exploit community engagement for a profit)

Time would be better spent contributing to an open source alternative like Athens!

Thank Ben :)

Roam's site[1] only mentions $165/yr. The 5 year plan is $500, but then... if you stop using it after a year, you would have paid $500 for 1 year of usage. If you're thinking of no lock-in, you need to see the monthly price, which is $15 month, way more expensive (for personal use) than anything notion has (free/$4/$8 per month)

[1]: https://roamresearch.com/