Self-hosted Webinar service software
A few suggestions:

BigBlueButton


  BigBlueButton is an open source web conferencing system for on-line learning. BigBlueButton enables you to share documents (PDF and any office document), webcams, chat, audio and your desktop. It can also record sessions for later playback.


BigBlueButton is free and open source.

OpenMeetings


  Openmeetings provides video conferencing, instant messaging, white board, collaborative document editing and other groupware tools using API functions of the Red5 Streaming Server for Remoting and Streaming.


Openmeetings is free and open source.

WebHuddle


  Designed with the end-user in mind—as well as the realities of corporate information technology resources—WebHuddle is easy to use and flexible in delivery and installation. To create a meeting today, simply click the log in button, create a profile, and follow the instructions for uploading content and conducting your WebHuddle virtual meeting. During the beta period, there is no charge to use the WebHuddle service.


WebHuddle is free during the beta period.

RHUB Webinar Appliance


  R-HUB gives you 6-in-1 web/audio/video conferencing and remote support server that YOU own and YOU control. Forever.


RHUB Webinar Appliance is a commercial product.