ZeroTier (ZT) is open source and free to use for most cases (commercial/proprietary use makes it not free).
It's a network virtualization platform that lets you connect to your devices with automatic end-to-end encryption. Think of it conceptually like a VPN, SDN, and SD-WAN all in one.
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Create and verify an account over at https://my.zerotier.com/
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Create a network https://my.zerotier.com/network