If you have a need to manage support for pay sites, software, services or anything else then there's a confusing array of options that are mostly paid.
A brand new option is a well developed web application called Free Scout.
Free Scout is production ready, it's not beta software. It is under active development and has a well thought out interface and workflow.
Features include:
100% Mobile-friendly.
Multilingual.
Seamless email integration.
Web installer & updater.
Starred conversations.
Push notifications.
Auto reply.
Saved replies.
Notes.
Pasting screenshots from the clipboard into the reply area.
Satisfaction Ratings.
Configuring notifications on a per user basis.
Open tracking.
Tags.
Edit / hide threads.
LDAP integration.
Search.
Check out
https://freescout.net
Free Scout is entirely open source, with the source code on GitHub here:
https://github.com/freescout-helpdesk/freescout
Like everything I post here I am more than happy to help people install or get up and running with open source software. I am not always instantly available but will be able to help you get going.