Hello,
I have been using for some years now the Slack chat system, in several Open
Source projects, but also the paid version on the companies I have been
working for, or customers.
So we can instant chat in channels or directly to members or group chat up
to 5 people.
We can transfer files. (I even use it to transfer from my Linux or Mac to a
Windows machine).
We can do video/voice calls.
We lose the history of chats after some time, because it is the free
version. Important conversations should be stored on some permanent medium
(like email/mailing list). We can apply for the Pro plan for free if with
less than 250 members.
In no way this is a replacement for the mailing lists.
This is an invitation link that will expire in 60days (or so):
https://join.slack.com/t/gretlgnuecono-vxh1344/shared_invite/zt-waoqek6r-...
Hope you find it useful.
Hélio