Entity Signal is described as 'Real Time Entity Framework (EF) and ASP.NET core. Make all of your data real time. Receive updates no matter where the object was created or edited. Uses existing ASP.NET core permissions system'. There are nine alternatives to Entity Signal for a variety of platforms, including Online / Web-based, Self-Hosted solutions, Windows, Linux and Node.JS. The best alternative is Firebase, which is free. Other great apps like Entity Signal are Etebase (Free, Open Source), RxDB (Free, Open Source), Pubnub (Freemium) and FeathersJS (Free, Open Source).
Etebase makes it easy to build end-to-end encrypted applications by taking care of the encryption and its related challenges. Think Firebase but encrypted in a way that only your users can access their data.
SapphireDb is an open source library that enables you to easily create your own application with realtime data synchronization. It extends your Asp.Net Core Application with EF Core and combines the advantages of firebase and .Net Core together.