VistaDB is licensed per developer site. This means whether you have five developers or twenty operating out of the same official corporate address you can all use one VistaDB Site License. If you have remote (teleworkers) they count as part of the official company address you associate them with. If you have developers working out of two sites you'll need two VistaDB Site Licenses, etc. With a site license you can install VistaDB on as many computers as necessary.
With some exclusions (see below, and for more detail the End User License Agreement (EULA)) you are free to redistribute VistaDB as long as you have purchased license(s) for your developers. In turn you can use it just internally, or redistribute it across the earth with your applications. The key requirement is that anyone compiling an application that references VistaDB have a valid license.
The exception is for products that merely wrap VistaDB but otherwise directly allow downstream developers to create their own applications with it. The classic example of this would be an ORM - it's intended to enable other developers to create their own applications in a faster way by making it easier to create and interface with the database. In these cases the VistaDB runtime libraries should not be shipped and the end-user should acquire their own license.
We're thrilled at the rich ecosystem of products that include support for VistaDB. If your product's primary purpose is data access - such as an ORM or reporting system - end customers will need to purchase VistaDB on their own to use it with your product. If in doubt, just reach out to us at support@gibraltarsoftware.com.