Recs.
Updated
With ASP.NET Core you can build web apps, web services, IoT apps, and mobile backends. It can be used with Visual Studio, or with Visual Studio Code, see article on Medium Getting started with ASP .NET Core.
ASP.NET Core enables client-side development with Razor Components and Blazor.
Read 8 .NET Technologies for 2022.
Also read 3 Fundamental Components of a Reusable .NET Microservices Platform.
SpecsUpdate
Pros
Pro JSON API's
From .NET Core 2.1 new APIs are added that make it possible to write JSON APIs that require less memory, using Span<T> and UTF8 strings, and improve throughput of applications like Kestrel, ASP.NET Core web server. See also Utf8JsonReader.
Pro JSON optimization
In .NET Core 2.1 and 3.0, new APIs are added that make it possible to write JSON APIs that require less memory, using Span<T> and UTF8 strings, and improve throughput of applications like Kestrel, ASP.NET Core web server. See also Utf8JsonReader.
Pro Built in Dependency Injection
Where in the old ASP.NET we had to rely on 3rd-party solutions, Dependency Injection is now built in.
Read Implementing an Effective Architecture for ASP.NET Core Web API.