Confluence

Real-time simultaneous editing
Ease of finding and organizing what I've written
Constantly adding new features
Integration with Jira and Trello is great, but also works as lightweight project management by itself

Honestly, they've fixed my biggest cons, like storage space (now you can buy a bigger plan) and they keep adding more things.
I think my colleagues would say there's still a learning curve, which is understandable, and I think Confluence has been changing the interface with more tips and features for new users (which is sometimes confusing for long-time users like me, LOL)
One big con is still the limited integration with MS Office. Confluence fully replaces the need for Word in most cases, so that's not a big deal, but I wish the Excel integration and/or the table functionality was better.
Also, printing is pretty tough when you have tables.

The best feature that this has is the extended Add-In marketplace. You can find the proper Add-In to express your ideas in the best way: Coding, Images or illustrations, animated gifs or videos, and even forms inside the documents and pages. From a user perspective, this is one on the easiest knowledge base software in the market, and also you have the bakcing of Atlassian. The process of the integration with our existing business logic was easy because we didn't have a strict knowledge base, but Confluence gave us the foundations to build one from scratch.

The export tools and options you have inside the platform are not good. The data isn't portable, so you can't migrate easily to another platform in case you want. The installation process was complex, but today, they stopped producing self-hosted applications, so you are obligated to use their cloud services, and it can be a problem if the company has a strict data policy, like restrictions in the phisycal storage of the data.

Confluence offers my company a unique solution for creating and organizing documentation and assets that need to be share amongst an entire team. In addition, it offers us a means to share some of those same documents and assets with our customers without any additional effort. Its advance permissions schemes allow you to dictate which users have access to which files, and its ease of use allows for quick publication and instant distribution. As we also use JIRA for project management, Confluence is a great complement for linking supplemental, more detailed files to ongoing projects.

Confluence word processing features are a bit rudimentary. While the application itself is easy to use, its feature limitations only allow for a certain level of detail and imagination when creating new documents. While it links seamless into the JIRA project management platform, it does come with an additional cost per user, which quick racks up your monthly Atlassian bill. For more advanced needs, an alternative platform may be a better fit.

Highly configurable and easy to use document templates, beautiful interface akin to using Medium, and deep integration with Jira Software and Jira Service Management are the features I find most useful. Recent changes to Templates to enable you to quickly search and preview available templates is incredibly helpful, as inline commenting while editing and being able to quickly convert anything into a Jira issue. Being able to use Confluence to defer service management requests by offering reporters the option of self serving an answer to their question/problem is a stroke of genius.

It's beyond irritating that exporting documents as a PDF is so horrendous out of the box. I also find the concept of Actions vs Jira issues confusing. I consistently find myself missing actions that have been buried in Confluence.