OpenBSD is a general purpose Unix operating system. It emphasizes security and correctness. OpenBSD runs on several different architectures. Swonk runs OpenBSD on x86, AMD64, Sparc64, HPPA, PowerMac, Arm and Arm64. Just because he can.
The OpenBSD installer gets a bit of flack because it is a simple text only installer. No GUI. This is typical of OpenBSD. No unneeded frills. Just the beef. The installer development concentrates on useful functionality, not looking pretty. It also means that doing an install over a serial console is no different to an ordinary install.
The install can be done from CD/DVD using the ISO images, from a USB drive, or from the network.
OpenBSD has the base install, which gives you a functioning operating system. It is basically POSIX Unix.
The ports and packages system provides applications. While there are not as many applications as some other operating systems, there are enough for most purposes.
OpenBSD uses its own http daemon. It's small, simple, and secure. Many OpenBSD daemons run as unprivileged users and chrooted to reduce the opportunity to exploit any vulnerabilites. The http daemon runs by default as user www, chrooted into /var/www.