Kokua and Koa are no longer offered.
From the Napili template, you can customize the appearance and functionality quite easily. You also have access to Salesforce Tabs + Visualforce.
Depending on your use case, you can chose from either one, as mentioned earlier both are "Easily" customizable if you know what you are doing.
The way to go for customizing your Lightning community is to Create a Custom Theme Layout Component for Communities
Additionally, you have several branding options to customize the look and feel of the community:
As you can see, next to Branding, you can add CSS rules to customize the whole of your community,and the settings allow you to further add customizations through Theme, Advanced, and so on: