Since this thread is already derailed (lol) and there's a thread about the theme here, I'll comment on this.
I'm pretty adamant about using only FOSS services, but I also accept that there's a trade-off that has to be made sometimes when it comes to outreach. That said, I think the crowd who are interested in this type of game jam are probably more willing to go out of their way to use open-source tools. I've chosen to draw a line about the chatroom because,
1. There are several good options that aren't proprietary.
2. A chat application is more personal.
3. I won't ask my teammates to use something proprietary. I'm the only member of my team on itch.io.
If there's an open-source alternative to itch.io that will do as good a job for outreach I'd also prefer it. I think it's worthwhile to work towards that. At the moment I'm not sure there is, and it might not be feasible to have an open-source game jam without it. Not sure how Liberated Pixel Cup did it, but they had some pretty big sponsors. So, if we want to solve that problem I think it'd be better if we helped rather than complain about it.
Is there any reason to prefer Discord over Gitter or Riot in the future? Let me know if you'd rather this conversation be somewhere else.