1. Power Apps

You can think of the Dynamics 365 applications that Microsoft supplies (Sales, Marketing, Service, Finance, Operations, Commerce, HR) as 1st Party Power Apps that all use the same underlying data platform, the Common Data Service.  
 
Power Apps then enables you to create your own Apps that also use the Common Data Service to store and secure data, which means they can also share your core business data from your 1st Party Dynamics 365 applications, without the need for integration.  
 
In addition, you can add pre-built 3rd Party Power Apps from the Microsoft AppSource, which will also seamlessly integrate with your existing data that is stored in the Common Data Service. Microsoft describes Power Apps as a high-productivity development platform for business apps, made up of four major components:

Canvas apps are apps you can build for web, mobile, and tablet. You start with the visual interface and define how do you want your users to interact with your data, whether from the Common Data Service or over 200 other data sources for which there are out of the box connectors. Uses can range from a simple holiday approval app, to an event check-in app, that your event staff can use to scan name badges to track event attendance, right through to creating a completely new interface for your 1st Party Dynamics 365 applications.
 
Model-driven apps enable you to build your own app, with a consistent interface, as used in Microsoft's own 1st Party Apps. You start with your data model, by deciding which core data and processes you want to use from the Common Data Service, and what do you want to add. Maybe you just want to combine data and processes from several of your 1st Party Apps, or you could create a completely new application.
 
Portals provide a way to create external-facing websites that allow users outside your organization to sign-in, create and access data in the Common Data Service. They are effectively a web CMS (Content Management System) built on the Common Data Service.
 
Common Data Service is the data platform that comes with Power Apps and allows you to store and model business data. It's the data platform on which Dynamics 365 applications (1st Party Apps) are already built, so if you’re a Dynamics 365 Online customer, your data is already in the Common Data Service.

Until recently Power Automate was known as Microsoft Flow. It enables you to automate business processes across your organization and lets you securely connect to on-premises data and cloud based services. 
 
For example, when a new record, email, tweet etc. is created, we can use Power Automate to trigger subsequent actions, create new records, respond, set alerts, or sync data with other systems. We can also add conditions, so we can ensure we only execute automation flows when certain conditions are met.
 
Existing functionality from the Dynamics 365 world like Business Process Flows and Workflows have been moved to Power Automate and are now Power Automate Flows.
 
Key features include:
Multi-step Power Automate Flows to automate repetitive tasks. For example, create a Flow to capture tweets and automatically add them as leads or cases in Dynamics 365.
 
Create approval requests using automated approval workflows to quickly respond to and process requests, from time off and travel plans to documents and sales opportunities.
 
Securely connect to on-premises data and cloud based services, so you can fully exploit the data you already have. You can also prevent sensitive data from leaving your company using built-in or customized data loss prevention policies.
 
RPA (Robotic Process Automation) enables users to record and playback human-drive interaction, similar to recording a macro in Microsoft Excel. (Also referred to as UI Flows).

Power BI is all about creating a data driven organisation and the democratisation of business intelligence within business organisations. It makes it easy to connect disparate data sets and transform and cleanse the data, to create a data model from which charts and data insights can be created and shared, including resurfacing data within your PowerApps or other websites and online applications. You can think of Power BI as Microsoft Excel Online, but with scheduled refreshes and a multitude of sharing and embedding options.

Power Virtual Agents allows you to create intelligent online chatbots to engage with your customers, partners, and employees. It can provide a first line of customer service and triage for common issues so that your sales and customer service staff can focus on complex requests and high-value interactions.

Using a guided, no-code graphical interface, powerful chatbots can be created without the need for developers. These virtual agents can be empowered to take actions, by building custom workflows using Power Automate, or creating complex scenarios using the Microsoft Bot Framework. 

Power Virtual Agents can be integrated with existing business solutions using hundreds of prebuilt connectors. You can then monitor and improve chatbot performance using AI- and data-driven insights available in an easy-to-read dashboard.