CLOQ is a web-based team timer that works without any setup. At this time, you don’t need an account or have to pay anything. It works best in multi-screen environment. Tablets or smartphone do work, but you currently have to work around the auto-lock of your display.
The timer works with as many participants as you want. People only need to access the link you have provided – that's it!
As a facilitator you have the power (and responsibility) to manage the timebox for all the other participants.
It is important you use the Share button. Else your participants will be able to manipulate the timer. Your participants can open a new browser window, open the link and set CLOQ as a small window to the side.
If you want some extended features (which are currently not integrated), you can use the free tool Flotato to generate a “native” macOS app.