Cisco WebEx, easily the most well-known of the apps on this list, is also a Java-based conferencing solution. Also available are mobile apps for iOS, Android, and Blackberry. Like the others, it offers all of the standard conferencing features within the free version and additional features if you upgrade. The free version is limited to 3 participants; upgrades to 8 or 25 people per meeting are available. Like Adobe Connect, WebEx also has Enterprise options for up to 500 people but they do not appear to offer on-site services.
Screenshot of Cisco WebEx app by Wally Bahny for TechRepublic