What solutions are available for creating your own webinar space?

Question

Programming

Hello!
There was a need to create our own service for holding webinars.
Good examples of what should be the output: myownconference.ru and clickmeeting.com
Interested in whether there are ready-made scripts / engines (paid and free) that can be taken as a base and manually overgrown with design and modified functionality? desirable cross-platform.
Only free ones were found on the Internet: bigbluebutton and openmeetings, other options are interesting