GenericRepositorySimple

As mentioned in the comments, avoid reinventing the wheel. If you are using any full ORM (the Entity Framework here), it itself serves as Repository as well as UoW. So, using ORM itself inline and bypassing both Repository and UoW is most recommended. Following are some good read:

https://ayende.com/blog/4784/architecting-in-the-pit-of-doom-the-evils-of-the-repository-abstraction-layer

http://www.primaryobjects.com/2010/03/17/using-the-nhibernate-repository-pattern-in-c-asp-net/

But, in some cases, you may still want to implement Repository. This allows you injecting the repository in your code making other part of the code testable. Even in that case, avoid using Generic Repository. It is considered an anti-pattern.

In that case, implement concrete repositories per Aggregate Root. Avoid Generic Repository OR just use it as base class for all your concrete repositories. More explanation could be found in this and this and this answers.

Your linked GitHub sample code looks good interface for Generic Base Repository class. Note that it exposes IQueryable GetAll();. If implemented in base class, this should be fine. Never return IQueryable from your concrete repositories. It violates basic purpose of Repository Pattern.