I'm not sure we use any software that you haven't heard of before. Having solid communication and project management tools are an imperative. We use HipChat (but Slack is great, too - probably better, IMO), GitHub, Zoom, Hangouts, etc. Been a while since I used Slack (my old job used it) but HipChat's integrated video call button is great. As a general rule, I opt for video call over audio only whenever possible. Being able to see who's currently online is also a must-have feature. Our PM tool is Workamajig, but for the purposes of being remote, any tool that can let you see the current status of any project, who's currently working on it, and any conversation threads surrounding it is a huge plus.
In short, any tool that enables and facilitates transparency, openness, and communication is worth your investment.
There are gimmicky tools/gadgets out there, too. Our office has one of those remote controlled robot-iPad-on-wheels things... but it doesn't get much use.
Yeah I don't think we plan on getting the iPad on wheels any time soon but I do want to put some effort into the little things that can make audio/video/connectivity better. We use Slack and are happy with the calling features. Slack also acquired Screenhero so I'm excited for some of those features to get more integrated.
The "robot-iPad-on-wheels" was actually a lifesaver for our company - we didn't have the discipline to avoid the water cooler conversations or instantaneous whiteboard sessions, so having the robot be able to 'overhear' the conversation was actually immensely helpful for the remote person.
We just switch from Slack to Discord. The voice channels add an "office environment" feeling to just speak when you have a question. And it also has all the chat features of Slack/HipChat. The only downside is no integrations so if you need that then Slack is your best bet.
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