Free ASP.NET hosting service is free, (sometimes) advertisement-supported web hosting, and is often limited when compared to paid hosting.

C# 8.0 and .NET Core 3.0 – Modern Cross-Platform Development: Build applications with C#, .NET Core, Entity Framework Core, ASP.NET Core, and ML.NET using Visual Studio Code, 4th Edition
ASP.NET Core 3 and Angular 9: Full stack web development with .NET Core 3.1 and Angular 9, 3rd Edition
C# in Depth, 4th Edition

Some companies provide free ASP.NET hosting for some period, so the user could test their services.

You could also receive free ASP.NET hosting for some period if you prepay for the hosting services. By example if you pay for 1 or 2 Years in advance, then you will receive 3 to 6 months of free hosting through price discount.