Customer Relationship Management (CRM) allow you to manage customers.
Fre plan allow unlimited users, unlimited contacts, shared inbox and ticket system. Look like a good system to use as shared inbox/helpdesk. They have google chrome extension, that integrate with gmail/google workspace so all emails get tracked in CRM with read notifications.
Free for upto 10 users. Helpdesk.
Bitrix24 is Open source CRM. Paid and Free Options available.