(I'm a founder at Heap.)
We get this question so frequently that we've created a page dedicated to answering it: https://heapanalytics.com/docs/other-tools. It describes how Heap compares to Google Analytics, Flurry, Mixpanel, and KISSMetrics.
At the core, Heap's main differentiator is that it automatically capture everything, such as clicks, taps, form submissions, and pageviews. This lets you analyze data retroactively, without writing any code. Every other analytics tool requires you to define events of interest upfront.
Feel free to ping me directly at matin@heapanalytics.com if you have more questions! Happy to go into more depth.