Here is an older and a newer thread about staff communication:
Staff Communication: How do you do it?
Throw Away Your Hostel Logbook - It's not working.
In my hostel now we use a very simple Google Doc spreadsheet. (Date, Your name, Comment) Beside the comment we have a column for each member of the team. Once they read the comment they mark the cell under their name to indicate they have read it. This way everyone is sure to get the same information. We also know who has received the information and who has not.
I worked on a team that tried very briefly to use Slack. It seemed pretty simple and straightforward, but it didn't really catch on and we abandoned it for some reason. I couldn't tell you why. Other hostel operators have told me that they love Slack and swear by it.
It seems like it's getting more common now for PMS providers to include a messaging system, but as far as I can tell this works better for one-to-one messaging (ex. for the person coming on shift after you) rather than communicating to the entire team.