Yes and no. It's primarily focused on centralizing data into a data warehouse / data lake rather than sending data out to other apps. Segment also pushes events into a warehouse but most of its functionality is about forwarding events to 3rd party apps. That said, you can use tools like getcensus.com to move data/events from an AWS-populated data warehouse back to other apps (disclosure: I'm one of the founders of this service).

I think yes, all these products -> https://segment.com, https://rudderstack.com, https://snowplowanalytics.com, https://fivetran.com, https://stitchdata.com, https://www.alooma.com, https://singer.io, https://www.holistics.io, can work as a pipeline, but some have more features than others.

This is a bit simplifying answer.

Founder of RudderStack here (we are an open-source Segment alternative)

Segment (or RudderStack) is primarily for routing event-data from your apps to multiple destinations (cloud SaaS, warehouse etc). On the other hand, AppFlow is for syncing data that lives on cloud applications with AWS products like RDS, RedShift etc. So, both the nature of data is very different (event-streams vs database update batches) and also the destinations where they are sent (multiple cloud applications + data-warehouse VS only datawarehouses/databases).

Segment also has a product similar to AppFlow called Segment Sources but that's not what Segment is known for. There are a bunch of other products in that space like Blendo & FiveTran.