Tabtastic provides a quick and simple general check in solution which syncs directly to your tab, and also provides a judge self-check in which allows judges to check themselves in and out at any time.
You can start check in by running the /checkin <hh:mm> command (e.g. /checkin 09:00), where the time is when you want your check in session to end. Tabtastic will then make a post in your configured announcements channel, notifying everyone that check in has opened. Participants simply need to click the tick react underneath the message, and they will be marked as checked in on your tab. You can then monitor check in status on your tab, and use it for the draw. Tabtastic will also send a warning 3 minutes before your check in is due to end, reminding everyone that it is closing soon. You can also use the --clean flag with the check in command to remove all current check ins before opening the session (e.g. /checkin 09:00 --clean), which can be useful if you want to run a general check in for each round, as most check ins last for 12 hours.
You can also create a judge self check in by running the /judgecheckin command in any channel. This will create a check in widget in the channel where you run the command, with a check in and check out emoji. Judges can then click either emoji to check themselves in or out, which will also be synced to the tab. Tabs do not generally apply this directly to your current round availability, so make sure to set your judge availability from check in on your tab. The judge check in widget can be used multiple times, and never expires, so if you want to stop it, just delete the message.