Knowledge base was a buzzword a few years ago. Few companies were evangelizing the idea of wiki technology and nobody was using it. Today, the landscape of knowledge base is totally different. All enterprises use some kind of wiki implementation that is there to share knowledge. They mostly use Confluence, but there are also other wiki solutions available, commercial and free as well.
Knowledge bases store information that you, as a developer, would write down in a paper notebook for your later reference, for example, the IP address of the development server, directories where to install the JAR files, what commands to use, what libraries you have collected, and why you use them. The major difference is that you write it in a formatted way into a wiki and it is available immediately for other developers. It is a bit of a burden on the developer to write these pages, and it needs some self-discipline first. Sticking to the example of the IP address of the development server and the install directories, you have to write not only the IP address of the server but also some text explaining what the information is, because the others may not understand it otherwise. It is also a bit of work to place the page with the information in the wiki system with a good name, linking it to other pages, or finding the appropriate position of the page in the tree of pages. If you were using the paper notebook, you could just write down the IP address and the directories on the first free page of the book and you would just remember all others.
The wiki approach will pay back when coworkers do not need to find the information themselves; you can find the information in an easier way because other coworkers have also recorded their findings in the knowledge base and, last but not least, a few months later, you find the information you recorded yourself. In the case of a paper notebook, you would turn the pages to find the IP address and you may or may not remember which one is the primary and which is the secondary server. You may even forget by then that there are two servers (or was it a double cluster?).
To have a long list of available wiki software, visit https://en.wikipedia.org/wiki/Comparison_of_wiki_software.