ASP.NET Boilerplate is a general purpose application framework especially designed for new modern web applications. It uses already familiar tools and implements best practices around them to provide you a SOLID development experience.
Orchard Core is an open-source modular and multi-tenant application framework built with ASP.NET Core, and a content management system (CMS) built on top of that framework.
Finbuckle.MultiTenant is an open-source multitenancy middleware library for .NET. It enables tenant resolution, per-tenant app behavior, and per-tenant data isolation.