There are a bunch of parishes in my diocese which use the MyParish app. It is… well. Convenient because there is one way to officially communicate. The bulletin is published there as well as on the website, announcements are made there, etc.

The pastor, secretary (who manages which groups are where at various times), and MC (who sometimes needs to know details) can all check in as they wish without actively participating. Each parish group has a group, and no one can see the conversations unless approved (the parish staff and lead volunteers have admin privileges).

It’s a pain because I’m sure we pay for it via the diocese or whatever, you can’t share files (I use Google Drive links if I need to share music)… and there’s no text formatting.

But people actually check it.

Otherwise, the default texting app is how people communicate. If it were up to me, I’d have a WhatsApp group; it is the best cross-platform app that would allow people to send PDFs directly, it has text formatting, and it has a usable desktop version. And then people could use just the same app in case they need to communicate outside the main thread. But it’s not.

And there will be some things for which paper has a role: perhaps this is micromanaging (or at least my expectations are calibrated strangely). I prepare out a document for each service of Holy Week with a reminder to bring a missal, the repertoire list, and then a break-down of what happens at the different points. That allows them to take notes; some people write down pitches, people mark call times and whatever else they need.

I do weekly emails as well. These remind them of any changes to the normal schedule and contain links to the Source and Summit practice tracks, practice tracks of anthems/motets (which I post on the parish YouTube channel if I need to make them) and pdf copies of the music for the week.
For Christmas and Holy Week I create Schedule/Rep Lists PDFs with all pertinent information and send them out a few weeks beforehand. I then print up-to-date Schedule/Rep Lists for them the week before, because there are always changes that have to be made "last minute."
Choir members look at these emails now a whole lot more than they used to, but I still make a point to remind them of important details (like the next rehearsal times, call times for Masses, or special music for upcoming Masses) at the end of rehearsal, because they are all volunteers who have families and I understand the chaos that can ensue if I don't communicate deviations from the norm at least 3 times in varying modes.
Choir members/cantors will communicate absences or concerns with me via email or texting, and cantor/choir scheduling works via email as well (I send out a list of dates about a month beforehand and my roster of cantors/choir sends their individual availability...I often have to hound one or two to get back to me in time).

We have a choir blog that is updated every time we sing, usually 12 hours in advance. Also email updates of the plan for the next few months, on a monthly basis and other updates as needed.
We also have a choir Watts app thing for those that have those newfangled 'phones.

Church choir - Informing and sharing between members - WhatsApp group.

The 60-member community choir I'm in also has
- a website (info for potential members and sponsors, and for posterity)
- a Facebook page, Insta acct (and Twitter acct, now defunct), for promoting concerts
- multiple WhatsApp groups (1 per section, and 1 for the committee).

Would either of these pay for or use a choir-specific platform? Nope.

ChurchSuite seems to be an e-mail and messenger service. I suppose I could use it for the choir e-mails, but it is so much easier to send messages from my personal e-mail account.

At St. Mary's in Akron, Ohio we use a app called GroupMe. We share music, upcoming events, practice times, request for prayers, etc. You can share documents, jpgs, pdfs, YouTube videos, mp3s, and probably someother stuff. You can private message someone if you want. It's quite handy and it's free!

i just use a simple email group on outlook. One message to entire choir