Is there any alternative OMS for Magento 2?

hi everyone, as i known Magento 2 has MCOM as OMS. My question is: is there any thing similar with MCOM? Similar i meant is: package of modules as MCOM connector to install to Magento 2, Package(source code: maybe php or whatever) for Management UI which can be installed in our own server and we can customize on our needs.

Functions we need:
Inventory management
Order management
Customer management

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There are some reasons that we can’t use Magento OMS.

Thank in advance.