Plugin: Invite
This plugin adds an additional link on customer dashboard - 'Invite a Friend'. User can use this link to send email invite to his friend. aMember creates a special coupon code for him. Coupon code will be included to email. You can alter email template for 'Invite Email Message' in plugin configuration.
You need to add Coupon brick to signup form and make it required. You may want to alter labels for this brick to 'Invite Code' aMember Cp -> Configuration -> Forms Editor -> (edit)
In case you use affiliate module then in plugin configuration you can enable option to generate affiliate coupon instead of ordinary one.
In admin interface in user profile you can find new tab - 'Invited Users' with list of invites done by this customer. aMember CP -> Users -> Browse Users -> (edit) -> Invited Users This tab will appear in user profile only in case of he already sent at least one invite email.
Also you can see list of all invited users at aMember CP -> Utilities -> Invite History
You can limit access to this feature by active user products aMember CP -> Configuration -> Setup/Configuration -> Invite