What is the difference among Cloud Logging vs Cloud Monitoring vs Stackdriver?

Let's start with some the history events:

Stackdriver the company was created in 2012 by founders Dan Belcher and Izzy Azeri. The company's goal was to provide consistent monitoring across cloud computing's multiple service layers, using a single SaaS solution.

and

In May 2014, the Stackdriver company was acquired by Google. An expanded version of the product (adding support for logs analysis, hybrid cloud support, and deep integration with Google Cloud) was rebranded as Google Stackdriver and was launched to general availability in October, 2016.

In March 2020 Google Cloud Platform (GCP) announced that it rebranded its Stackdriver monitoring and logging platform to be part of its new Google Operations platform. This rebrand included renaming Google Stackdriver Monitoring to Google Cloud Monitoring and Google Stackdriver Logs to Google Cloud Logging.

In a few words, Google Cloud Monitoring and Logging are successors of Google Stackdriver monitoring and logging, as a result users have more unified experience in the Google Ecosystem. To find more details you can have a look at the documentation Operations (formerly Stackdriver) and Release notes.

To compare Cloud Monitoring and Cloud Logging you can check documentation:

• Cloud Monitoring collects metrics, events, and metadata from Google Cloud, Amazon Web Services (AWS), hosted uptime probes, and application instrumentation. Google Cloud's operations suite ingests that data and generates insights via dashboards, charts, and alerts.

• Cloud Logging allows you to store, search, analyze, monitor, and alert on logging data and events from Google Cloud and Amazon Web Services.