[LinuxBender]

What type of business is this for? While I am not a fan of it, I found most developers liked Slack. The general consensus I received when trying to switch to an internal chat system was "You can take slack from our cold dead hands". This was in a financial company with a lot of developers. Compliance were OK with Slack after we had them add a lot of features, audit capabilities and limits.

For non developers people seem to like Discord for the freedom, options, ability to chat with whomever. It's not great in terms of compliance in a public company but maybe your company is small and this is not an issue.

The natural transition from Skype would be Teams and should be free if you are a small group. It is also free if you buy O365 or whatever they are calling it now. I can't keep up with the name changes.

Without understanding your business model it is hard to suggest anything that fits into your regulatory and audit requirements. Beyond that it would also matter what you put in your SOC1/SOC2 documents and what policies and procedures they reference.