What's the difference between a marketplace, an aggregator, and a platform?

A lot...

My (simple) definitions:
Marketplace: Middlemen who actively facilitate liquidity on two sides, aid in discovery, and handle payment.

Platform: Middlemen who offer tools for content creation and a centralized location for supply to live.

Aggregator: Middlemen who serve as a search engine across disparate supply, and often maintain a valuable data catalogue.

What they all have in common
Middlemen
Take Rates
Network Effects
A minimum of two sides they have to connect

Where they differ:
I look at the four main factors below when comparing the three business models.
Here are some relative stack rankings.
They are by no means iron clad characteristics.

Payment responsibility: Marketplaces > Platforms > Aggregators
Demand generation: Marketplaces > Aggregators > Platforms
Required resources: Marketplaces > Platforms > Aggregators
Take rates: Marketplaces > Platforms > Aggregators