ThemeBuilder is available for installation through the Atlassian Universal Plugin Manager (UPM) Find New Add-ons screen.
You can also download the app from the Atlassian Marketplace, and then install using the UPM Manage Add-ons screen.
There is a trial version, but after 30 days the app needs to be licensed.
The ThemeBuilder Editor package contains two apps:
Adaptavist ThemeBuilder Editor
This app allows the creation and editing of skin data which can be used by the Engine. For the Engine to be able to pick up and use data created by the editor, the editor must be fully licensed.
Adaptavist ThemeBuilder Engine
This app takes the data created by the editor and uses it to present a themed experience to the end user.
ThemeBuilder is a commercial app licensed via Atlassian through the Universal Plugin Manager (UPM). After installation you will find that there are several plugins made available in the list of installed plugins, each of these plugins is capable of being licensed separately, however they do not all require a license.
If the ThemeBuilder Editor has a valid license, then the ThemeBuilder Engine is automatically licensed too.
The Engine may show as Unlicensed if you have licensed through the Editor. As long as either Engine or Editor has been licensed, and the ThemeBuilder app is working normally, then this can be ignored.
To obtain a license you first need an Atlassian ID, you can then either purchase a license or generate a free trial through the UPM, once it has been correctly configured, or you can purchase the license through the marketplace and then install the license by pasting the text downloaded from the licenses page in your My Atlassian account.