We use some other tools, but Slack is the dominant one by far. We don’t use email at all for communication within the company. We are now using Slack for calls too. For calls, it is sometimes unreliable.
We use Mixpanel for direct user follow up marketing emails. We are pretty new to them, but we really like them because they provide pretty thoughtful built-in management tools.
We use MailChimp for newsletters. The pros are that the interface is very nice, they have good analytics on the emails and it is easy for the receiver to subscribe and unsubscribe. The con is that it is not customizable from a developer standpoint.
The annoying thing about QuickBooks is that the online version is not compatible with the desktop version. Also, there is no backwards compatibility. Our accountants were using a different version and we had a lot of problems when we tried to synchronize with them.
AHA! is an idea and bug tracking tool, complementary to Pivotal Tracker. It is a great place to exchange ideas; employees and users can also both report bugs in it. It doesn’t have good project management tools, though, so we have to then convert ideas and bugs into tickets in Pivotal Tracker.
We keep all of our projects in Pivotal Tracker--we measure points every week. We have tried everything and it is by far the best project management tool. Unfortunately, if you are not an engineer, it takes a while to get used to.