It's also a very good idea to use tools and methods that are consistent with your end goal! If you're an open community, for example, it's best to use open tools. If, say, you adopt Slack for your communication (as many open communities do, unfortunately), you're undermining an open culture - there's some real dissonance in forcing your potential contributors to agree to 3rd party proprietary terms to participate in your open community (and the fact that you're giving a third party total control of your community's collaboration).
Yeah, I use Rocket.Chat daily (and manage a couple instance for other organisations) for work. I have also used Slack. To be honest, I think Rocket.Chat's quite a lot better. I think Mattermost, Zulip, Riot, and other open source options also have various advantages. To be honest, I tend to leave communities who don't offer an open source options instead of Slack, because to participate in Slack you have to give up a lot of your freedoms to the Slack corporation, as well as control of your community's data. If you don't pay for it, you also have a message limit of 10,000, after which point, your messages silently disappear. That sucks if you value a record of your community's or company's collaboration.
It's also a very good idea to use tools and methods that are consistent with your end goal! If you're an open community, for example, it's best to use open tools. If, say, you adopt Slack for your communication (as many open communities do, unfortunately), you're undermining an open culture - there's some real dissonance in forcing your potential contributors to agree to 3rd party proprietary terms to participate in your open community (and the fact that you're giving a third party total control of your community's collaboration).