The reason we do not have built in tools for Kartra is that they lack some basic functionalities such as:
a. You cannot show custom fields in the emails (so they would not show your webinar title, time & date or webinar link).
b. You cannot add dynamic variables to links so it would not allow you to add the link that allows people to automatically login to their webinar.
We are however working on a marketing webhook functionality, that will allow you to integrate with any autoresponder in an easier way, but in the meantime, you can do something like this.
As soon as things change with Kartra we will immediately add built in native integration. We are looking forward to offering that.