I love it, especially the iPhone and Android integration. When someone is working over the weekend and they have a tech question, it's so easy to check back, and when you're really "out of the office," you can turn the notification off. Slack as a service is pretty basic. It's just a text and chat room. We only use a few channels. We can see changes across our entire source code from different ventures and different projects. It just keeps you in the know.
As we’ve scaled, the contents of our mailing list have really diverged. At first it was just a few people who got everything, so we used Google Docs to manage them, but then the list just grew too big. This is especially true for our investor and technical lists; they both get different types of information from us, so we needed a better way of keeping track of them. I picked MailChimp because I was familiar with it. It was cheap enough that we didn't care much beyond that.
We picked Justworks because they also do all of our taxes. It was an easy and cheap way to handle everything at once. The administration is super simple; you just upload your paperwork and they handle everything for you. We don't really have the time to talk with an accountant or track everything ourselves, so it seems like a great solution. Before Justworks, we had to push all our administration stuff onto one employee.
It sucks, but there's nothing better out there. It's super complex, but the alternatives are all too simplistic. I think it's just a complicated problem in general. There might be better solutions out there, but I just don't know them. It feels like the complexity gets in the way of the workflow.