Unsealed.Fody (nuget): Use this addin to unseal sealed types. The most obvious usage of this is when working with F# records and an ORM like Entity Framework or NHibernate. Or if you want to create a dynamic proxy.      All of the previously listed scenarios require you in some cases to have an object can be proxied, requiring virtual properties which aren't possible when a type is sealed.
Keywords: ILWeaving|Fody|Cecil|F#|Unsealed|DynamicProxy