Summary

OpenBSD has its own FTP server called ftpd.
It's sufficient to transfer files among hosts in a simple and secure way.

How To Use

ftpd is installed as a daemon in OpenBSD as the OS is installed.
In order to use it, run rcctl enable and rcctl start, and it's almost done.

Step 0: Before Configuration

The daemon is disabled by default:

$ doas rcctl check ftpd
ftpd(failed)

Step 1: Enable Daemon

$ doas rcctl enable ftpd

* Note: Here, /etc/rc.conf.local is updated:

$ cat /etc/rc.conf.local
ftpd_flags=

Step 2: Start Daemon

$ doas rcctl start ftpd
ftpd(ok)

FTP server is now running.
As long as there is no network issues, you can establish ftp connection to the server 😉
* Note: Accessing as root is forbidden.

Reference: Additional Configuration

OpenBSD provides us several files, that is several ways, to add more configuration about such as chroot and authentication.