Well there are modular synthesizers, groovebox synthesizers and synthmodules which don't have a keyboard on them, only some knobs, some sliders, buttons and usually a lcd screen.
Until recently I've just been a singer, but now I'm picking on to other instruments, I'm doing more on the piano, a little bit of guitar/bass/tuned percussion. And I'm doing drums. So soon I'll be able to very comfortably say I can write a traditional rock song (two guitars, a bass, vocal and drum), and then record it completely on my own.