LWC Framework Is Open Source

Yes,Salesforce announced open sourcing of the Lightning Web Components framework,Refer

As shown below,Lightning Web Components framework doesn’t have

dependencies on the Salesforce platform. Instead, Salesforce-specific services

are built on top of the framework.What that layered architecture means

is that you can now use the Lightning Web Components framework to

build web apps that run anywhere.

Differences Between Building Lightning Web Components on Lightning Platform and Open Source ?

In short, for faster development and to avail other benefits LWC on the Salesforce Lightning Platform is the best choice.Refer

LWC on lightning & Open Source feature comparison