I couldn't do anything in an open office without blocking the noise. Visual distractions are almost as bad but are harder to block.
I use sox to generate audio. It is available for win/Mac/Linux. I set it for 90 minutes of brown noise which gives me a reminder to get up and walk around when it ends. I believe it can generate white or pink noise if you prefer.
>play -n synth 90:00 brownnoise brownnoise