I used Slite (YC W18) for keeping my personal knowledge base. The reasons I use Slite other than Google Keep or Google Drive are because it's simple to use, it's like Slack so very easy to rearrange and organize like the structure that I want (this is the most important part of knowledge base IMO), and it supports markdown better than google docs (most of my knowledge base are software development related, so I'm a big fan of markdown).

Last but not least, for business presentation, I'll link the Google Slides on the Slite so every information will be centralized and organized from Slite.