Hello Alexey,
The Joomlatools Platform is minimal version of Joomla targetted at enterprise projects. It includes the core functionality of Joomla. Everything you don't need to run Joomla has been removed or moved into separate installable Github repo's. Less code means less potential for security issues and means a faster Joomla. To get an overview of the platform please check :
https://www.joomlatools.com/developer/platform/
You can use Joomlatools Platform with almost all third party extensions. Only extensions that don't follow the Joomla API's might fail, for example extensions that don't use the JPATH_ defines correctly. (since the platform changes the folder structure of Joomla).
The goal of the platform is to focus the administrator on content management and not on configuration management, which is a task for a developer. Instead of using the UI for installing extensions and managing things like cache cleaning and checkout, all this functionality has been moved into our Joomlatools Console:
https://www.joomlatools.com/developer/tools/console
Everything for the platform is freely available through Github, there is no special "payed" release.
Does that help you?
Johan