I work on Guilded (
https://www.guilded.gg), a tool for gamers to organize their teams, kind of like Slack + Google Docs + Calendar + Zoom. While you’re not gamers, it would directly address your use case (chat, RSVP to events, share photos, find common availability, host shared docs, have video calls, etc) for free in a single tool. It admittedly has a higher learning curve than a simpler basic chat app like Discord or Slack due to having more features (unused features can be disabled).
I’ve spent a lot of time thinking about different messaging tools and talking to people about their needs. I agree with other commenters that the _easiest_ (not necessarily best) and recommended solution will be whatever most people are already using, whether that’s an iMessage group, GroupMe, Telegram, or whatever. Getting people to use a new platform is a difficult problem because it only takes 1 person to refuse to force the whole group back to the status quo. If you will be adopting a new platform, then and only then would I worry about which one is “best.” Everyone (including me) will have strong opinions about the one they’re using being the best, so I can only share my experiences here…
While Slack is a solid option and I do use it for a couple groups, a big downside of the free plan is that that messages in lesser used channels or DM’s will disappear as discussion progresses in another channel, which can be very frustrating if you need to reference the last thing sent later. If you only need chat, Discord is a decent option as some people may already be using it, but you’ll want to train the group how to identify and avoid falling victim to the various scams plaguing Discord now. The ideals behind Matrix and similar distributed messaging apps are excellent, but in practice, they are not approachable for non-technical audiences, don’t provide any particular benefit for your use case to make the learning curve worth it, and are more likely to create a splintered group.
Let me know if you have more questions or what you decide, whichever way you go! Always curious to hear about the decision making process… neil@guilded.gg