You may choose to access Google+ through third-party applications (e.g. non-Google websites) by authorizing these applications to access all or part of your Google Account via the Apps connected to your account page. The developer of the application may have access to your email address and to the content you have access to in Google+ (such as content friends have shared with you). The developer may also request additional information from you, such as your location for mobile features of Google+. You can revoke the developer's access to your Google Account at any time by visiting this settings page.
App providers (such as game providers) may send you notifications directly. You will need to contact the app provider to change the type and frequency of notifications they send to you. If your connections use apps, those applications may gain access to content and information about you that those friends can access.