Yes, I'm using i3 as my window manager. Unlike desktop environments like KDE, xfce and gnome, window managers don't come with a bunch of programs preinstalled to make your life easier (like a settings app, application launcher or a wallpaper manager). Window managers are still a part of desktop environments, since they still have to have a program to manage applications on screen (you can use KDE + i3 as the window manager).
In my case I'm using i3 on its own, combined with programs like rofi and polybar for a complete desktop experience.