* [frp](https://github.com/fatedier/frp) [![frp github stars badge](https://img.shields.io/github/stars/fatedier/frp?style=flat)](https://github.com/fatedier/frp/stargazers) - Seems to be a pretty comprehensive open alternative to ngrok.
* [ngrok 1.0](https://github.com/inconshreveable/ngrok) [![ngrok 1.0 github stars badge](https://img.shields.io/github/stars/inconshreveable/ngrok?style=flat)](https://github.com/inconshreveable/ngrok/stargazers) - Original version of ngrok. No longer developed in favor of the commercial 2.0 version.
* [localtunnel](https://github.com/localtunnel) [![localtunnel github stars badge](https://img.shields.io/github/stars/localtunnel/localtunnel?style=flat)](https://github.com/localtunnel/localtunnel/stargazers) - Written in node. Popular suggestion.
* [inlets](https://github.com/inlets) [![inlets github stars badge](https://img.shields.io/github/stars/inlets/inlets?style=flat)](https://github.com/inlets/inlets/stargazers) - Open source ngrok alternative. Has pro option.
* [sshuttle](https://github.com/sshuttle/sshuttle) [![sshuttle github stars badge](https://img.shields.io/github/stars/sshuttle/sshuttle?style=flat)](https://github.com/sshuttle/sshuttle/stargazers) - Open source project originally from one of the founders of Tailscale. Server doesn't require root; client does. Explicitly designed to avoid TCP-over-TCP issues.
* [chisel](https://github.com/jpillora/chisel) [![chisel github stars badge](https://img.shields.io/github/stars/jpillora/chisel?style=flat)](https://github.com/jpillora/chisel/stargazers) - SSH under the hood, but still uses a custom client binary. Supports auto certs from LetsEncrypt.
* [expose](https://github.com/beyondcode/expose) [![expose github stars badge](https://img.shields.io/github/stars/beyondcode/expose?style=flat)](https://github.com/beyondcode/expose/stargazers) - ngrok alternative written in PHP.
* [teleconsole](https://www.teleconsole.com/) [![teleconsole github stars badge](https://img.shields.io/github/stars/gravitational/teleconsole?style=flat)](https://github.com/gravitational/teleconsole/stargazers) - SSH-based, but uses special client script. Focused on forwarding SSH console sessions, but can also forward ports.
* [go-http-tunnel](https://github.com/mmatczuk/go-http-tunnel) [![go-http-tunnel github stars badge](https://img.shields.io/github/stars/mmatczuk/go-http-tunnel?style=flat)](https://github.com/mmatczuk/go-http-tunnel/stargazers) - Uses a single HTTP/2 connection for muxing. Need to manually generate certs for server and clients.
* [sish](https://github.com/antoniomika/sish) [![sish github stars badge](https://img.shields.io/github/stars/antoniomika/sish?style=flat)](https://github.com/antoniomika/sish/stargazers) - Open source ngrok/serveo alternative. SSH-based but uses a custom server written in Go. Supports WebSocket tunneling.
* [PageKite](https://pagekite.net/) [![pagekite github stars badge](https://img.shields.io/github/stars/pagekite/PyPagekite?style=flat)](https://github.com/pagekite/PyPagekite/stargazers) - Comprehensive open source solution with hosted options.
* [Crowbar](https://github.com/q3k/crowbar) [![crowbar github stars badge](https://img.shields.io/github/stars/q3k/crowbar?style=flat)](https://github.com/q3k/crowbar/stargazers) - Tunnels TCP connections over HTTP GET and POST requests.
* [slt](https://github.com/inconshreveable/slt) [![slt github stars badge](https://img.shields.io/github/stars/inconshreveable/slt?style=flat)](https://github.com/inconshreveable/slt/stargazers) - Open source TLS proxy from the creator of ngrok. Supports SNI.
* [tunneller](https://github.com/skx/tunneller) [![tunneller github stars badge](https://img.shields.io/github/stars/skx/tunneller?style=flat)](https://github.com/skx/tunneller/stargazers) - Open source. Written in Go.
* [SirTunnel](https://github.com/anderspitman/SirTunnel) [![SirTunnel github stars badge](https://img.shields.io/github/stars/anderspitman/SirTunnel?style=flat)](https://github.com/anderspitman/SirTunnel/stargazers) - Minimal, self-hosted, 0-config alternative to ngrok. Similar to sish but leverages Caddy+OpenSSH rather than custom server code.
* [StaqLab Tunnel](https://tunnel.staqlab.com/) [![staqlab github stars badge](https://img.shields.io/github/stars/abhishekq61/tunnel-client?style=flat)](https://github.com/abhishekq61/tunnel-client/stargazers) - SSH-based. Client is open source. Server doesn't appear to be.
* [ngrok 2.0](https://ngrok.com/) - Probably the gold standard and most popular. Closed source. Lots of features, including TLS and TCP tunnels. Doesn't require root to run client.
* [Tailscale](https://www.tailscale.com/) - [![tailscale github stars badge](https://img.shields.io/github/stars/tailscale/tailscale?style=flat)](https://github.com/tailscale/tailscale/stargazers) Built on WireGuard. Easy to use. Doesn't include an HTTPS proxy on the public side, but could be combined with nginx/Caddy/etc. Some [code](https://github.com/tailscale) available, but I'm not sure what the implications of the custom license is.
* [Packetriot](https://packetriot.com) - Comprehensive alternative to ngrok. HTTP Inspector, Let's Encrypt integration, doesn't require root and Linux repos for apt, yum and dnf. Enterprise licenses and self-hosted option.
* [Lynk](https://lynk.sh/) - Advertises itself as a cheaper, faster, self-hostable (but not open source) alternative to ngrok. [Blog post](https://medium.com/@shivanshvij/building-a-better-ngrok-dbc104754822).