Google Analytics is the gold standard.
We use Segment on top of Google Analytics. It made Google Analytics far more valuable for us. Tracking events is far easier to manage with Segment.
We use InsightSquared on top of Salesforce to get insights through the pipeline.
Salesforce is an industry standard. If I had to do it all over again, I would be smarter about how we integrate all of our tools with Salesforce. I would have developed everything with Salesforce in mind. Salesforce needs an administrator because if you do not have someone curating it, it can become very uncanny. We had to set up several rules to be able to make Salesforce work for us. Even though it is very complex, I would definitely recommend it for startups as well.
Stripe is awesome. Before Stripe, setting up credit card payments was a nightmare. Stripe makes it so easy. If you think that it is too pricey, know that with another tool you will end up paying anyways in developer time.
Zenefits makes administration completely automated. It removes a lot of friction in the onboarding process. The fact that you can set up emails and notifications is very useful. It is very simple to use and makes everyone’s life easier.
Slack is empowering and has many features. We work with the mantra that there should be a single source of truth for every department. Slack is the app that everyone has opened at all times so we ended up building our own slash commands (like /report) so people do not even have to log into other applications to get information.
We used to use Paychex. We switched to Gusto because it puts the power into everyone's hands. Each individual is responsible for their own account. Employees can download their own W2’s and paystubs. The interface is very easy to use.
JIRA is similar to Salesforce in the sense that it gives you enough rope to hang yourself with. At the beginning we spent a lot of time on the settings level, trying to establish how we should use it. After a while, we realized that that way was not working and we had to do it all over again. We had to create documentation on how to use it. At the beginning, it can be frustrating but if you take the time to set it up according to your needs, it becomes incredibly empowering. It is so powerful and has so many options.