Customer Relationship Management (CRM) allow you to manage customers.
HubSpot
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.
Agile CRM
Free for upto 10 users. Helpdesk.
Bitrix24
Bitrix24 is Open source CRM. Paid and Free Options available.
https://www.bitrix24.com/uses/free-open-source-crm-software.php
See ERP