Ask HN: open source ticket / helpdesk system?

Hi I'm looking for a good open source ticke / helpdesk system.

With the following characteristics:

1. Able to receive tickets by mail or web. 2. Able to escalate tickets according to rules. Like: reassign this ticket if no comment in 12 hours. 3. Ideally would allow to convert tickets to github issues.

Thanks in advance :-)