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
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Download ZT on your devices. https://www.zerotier.com/download/
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Add your devices to your network as members (2 or more to test it out!).
SSL:
curl -s https://install.zerotier.com | sudo bash
sudo zerotier-cli status
sudo zerotier-cli join <network-id>
sudo zerotier-cli leave <network-id>
sudo zerotier-cli listnetworks