Parallel packaging helps in packaging apps for multiple platforms simultaneously.
To get parallel packaging add-on link, kindly create 2 packages for any platform at the same time and then open any third platform and click on "Increase parallel Packaging Limit"
Else please click on below link:
With purchase of 1 Parallel Packaging Add-on, it includes "+1 Parallel Packaging Capability"
E.g. By default User gets 2 packaging limit, by purchase this Add-on User can increase his/her Parallel Packaging limits. So user can now Package for 3 platforms simultaneously.