Discord
https://discordapp.com/

It was designed for gamers but many organizations are using the text function for communications. You can set up different "channels" for tow pilots, instructors, board, etc. Users have privileges to gain access to information.

Plus the voice chat function makes it easy to have a safety meeting or other meeting without craming everyone in the clubhouse or the Golden Corral.

Plus Plus it also is available as a phone app with all of the same features so you do not even have to have a computer!