Azure Active Directory Business to Business (B2B) is a feature on top of Azure Active Directory, which enables organizations to work safely with external users. To be added to Azure B2B, external users don't need to have an Microsoft work or personal account that is added to an existing Azure AD tenant. All sorts of accounts can be added to Azure B2B. You don't have to configure anything in the Azure Portal to use B2B; this feature is enabled by default for all Azure AD tenants.
Azure B2B is integrated with Office 365 for external sharing. It also provides APIs that can be leveraged inside custom applications to let both internal and external users authenticate.
Azure AD Free features are available ...
