Caddy uses Apache License 2.0
However, using their build server for commercial purpose is not free.
Yes, it is! Caddy is licensed under Apache 2.0, which requires attribution and stating changes made to the code when forking it, using it in your own projects, or distributing it. Subscriptions, on the other hand, are for non-personal use of our build server, which is different from Caddy itself. The build server creates custom builds of Caddy for you.
It also mentions -
If you download Caddy's source code and build it yourself, you don't need a subscription. Only commercial use of our download page requires a subscription. Keep in mind that if you build from source, you will have to manage Caddy plugins on your own.
So my Questions are -
How to create custom builds of Caddy without their build server?
How to manage Caddy plugins manually?