[weby]

We use a google sheet with seconds going down and people in initiative order sideways.

We have it on a monitor at one end of the table for easy viewing and one person in put in charge of updating it, but people can and do also look and edit it directly from their laptops.

So if there is a 3 second action it is put in the sheet in those 3 seconds and so on.

As for making things run smoothly, we have a few things/rules that each help in addition, some more others less:
-A quick action bonus: any action gets +1 if the description, rolling and any map movement for it is done within 10 seconds of their turn coming up.
-No taking back quick actions: 1 second is such a short time that you cannot cancel an action during it, you can stop a longer action at the next second though.
-No too long thinking on own turn, as there is no time to do too long analysis in one second, after 1-2 minutes there is a warning from the GM and then about one minute later if the action is not ready, their action was a "do nothing".
-Simplified movement: We use a simplified map movement and facing taking some of the fiddly bits of those things away.