Two products that I have seen rising in Knowledge management domain (Personal and Team ) are

Notion : https://www.notion.so/
Notion is something that I use on a Daily basis and within a month we have replaced more than 6 saas offerings with just Notion.

Guru : https://www.getguru.com/
The traditional concept of a knowledge base or “wiki” is becoming obsolete. Next-generation products unify information and contextually deliver knowledge directly into existing workflows. Guru is one company that has emerged as an early leader in this space.

There are a few things to balance with documentation:

• Making the content easily reusable by support teams to speed up replying to tickets
• Publishing the content online to anyone searching for the product plus the issue online
• Letting anyone in the company add/update/edit documentation to keep it generally fresh

The easiest way to accomplish the first is to use the documentation tool built into your help desk or customer support tool. So if you’re already using Salesforce Service Cloud, Salesforce Knowledge might make the most sense. If it’s anything like what Desk’s documentation tools were like before it was acquired by Salesforce, it should get the job done.

Otherwise, you can publish Confluence wikis publicly, either as read only or as an actual wiki that your customers could help edit (though that seems like it could get messy fast). If you already are writing internal documentation in Confluence, that may be your easiest route. One downside here though is that you can’t use custom domains with Confluence’s cloud app yet, so you would need to have your documentation on a separate domain (which works fine from an access perspective, though doesn’t help your company’s SEO rankings as much as having documentation on your domain could). Or, in the same way, you could expand your use of Paligo to cover non-technical documentation.

Essentially, if not adding new steps and tools to your team’s workflow is most important, any of those options would keep documentation inside stuff your team is already using. There’s no perfect solution, and frankly any CMS could be used to publish documentation (including a WordPress or Ghost blog, if you wanted, or any of the many documentation-specific tools), but using something you already are using and just adding extra processes around publishing could be the fastest way to get started.

If we're talking public/client facing I'd go with docusaurus or something else that lives as close to code as possible. Versioning is also a must for rapidly changing projects, and keeping the docs up to date.

For our internal project documentation, we use Confluence (https://www.atlassian.com/software/confluence). For customer facing Knowledge Base, we have been using Zendesk (www.zendesk.com) for quite some time. We were looking at switching to Intercom (www.intercom), but the articles seemed more organized at Zendesk. While Intercom is great for client conversations and chat, their knowledge base seemed very blog-like. So we have decided to stay with Zendesk for Product Documentation & Knowledge Base.

We have been using https://www.gitbook.com/. You can hook it up to your domain in the free plan (we are serving ours at https://docs.atlantica-app.com/ for example). Simple and clean interface with some cool versioning features (git-like as the name implies).

We as well are using Zendesk for providing knowledge base to our consumers. Super happy about it.

Archbee and Clickup are both used by small companies for public-facing docs, in addition to internal notes, collaboration, and formal docs. I don't think either of them would scale at all though.

Helpjuice (https://helpjuice.com/) was great and very feature rich when I used it. It's not cheap if you're just starting out though. If you wanna go cheap, Notion, like many others have already said, is stupid simple.