Open source
ABP
Open-source app platform for .NET. DDD, modules, multi-tenancy, SaaS module included.
About
Application framework on top of ASP.NET Core, built for line-of-business and SaaS apps. Modular DDD architecture, multi-tenancy, identity and account modules, payment and SaaS modules, distributed event bus, background jobs. UI options: Angular, Blazor or MVC. Free community edition with a commercial Pro tier on top.