I wrote SSH into your private machines from anywhere, for free, using Cloudflare Tunnel in April which led to a lot of discussion on Hacker News. A lot of people started mentioning alternatives (Tailscale, ZeroTier and issues with Cloudflare).
By the end of this post, you'll be able to run:
ssh $machine_name from anywhere in the internet-connected planet, using SSH keys. It is free and requires no future maintainance. This guide uses Cloudflare Tunnel, a service by Cloudflare with a free-tier. It will filter traffic to your machines through Cloudflare's network, including authenticating you. Because of this, your machines won't directly be exposed to threat actors and "1337 haxors".
This was discussed on Hacker News.