The core purpose of a product analytics tool is to analyze user behaviour and understand how users interact with your product.
The data powering PA tools comes in the form of event data from your website and apps.  You can also send event data from external apps but doing so bloats PA tools with too many events and can also result in data quality issues.
PA tools primarily cater to Product and Growth teams where:
Product teams are able to improve product development by prioritizing features that are used and killing the ones that are not
- And Growth teams are able to improve onboarding, activation, and retention by visualizing the user journey and identifying points of friction
Mixpanel, Amplitude, and Heap are leaders amongst PA tools whereas PostHog, Indicative, and Rakam are gaining steam. They all serve the same purpose and all of them integrate with popular tracking solutions (like Segment and RudderStack).
PostHog is an open-source alternative to Heap as they both offer codeless event tracking, also known as implicit tracking or autocapture.
Indicative and Rakam, on the other hand, are warehouse-centric with support for popular data warehouses (like Snowflake, Google BigQuery, and AWS Redshift) as well as Snowplow as data sources.
With the rapid adoption of the data warehouse, more and more companies are experiencing the benefits of making the warehouse the source of data for both PA and BI tools (more on this below).