Some of the top Open Source templates for setting a strong infrastructure base for your SasS application. This framework provides the base for getting started quickly doing all the infrastructure part needed to handle multitenancy.
ASP.NET Boilerplate — Web Application Framework
ASP.NET Boilerplate is a general purpose application framework specially designed for new modern web applications. It uses already familiar tools and implements best practices around them to provide you a SOLID development experience.
ASP.NET Boilerplate works with the latest ASP.NET Core & EF Core but also supports ASP.NET MVC 5.x & EF 6.x as well.
abp — Preview
It is also an open source web application framework for asp.net core. It is is an entire rewrite of ABP Boilerplate mentioned above
SaasKit is a .NET toolkit for building SaaS (Software As A Service) applications.
The goal of the project is to help developers build SaaS products without getting in the way. It aims to be platform agnostic and as simple to use as possible.
Finbuckle.MultiTenant is a multitenancy library for ASP.NET Core 2.1+. It provides functionality for tenant resolution, per-tenant app configuration, and per-tenant data isolation
ASP.NET Core multi-tenant web application foundation with management for sites, users, roles, claims and more
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 application framework.