9. A computer program product comprising a non-transitory computer-readable storage medium containing computer program code for: extracting features from an application linked to an online system, the application used by users of the online system and configured to post content to the online system, the application operating independently of and external to the online system; applying a trained model to the extracted features of the application to generate a quality score for the application, the trained model is trained by identifying features extracted from a set of training applications, quality scores are manually assigned to each of the set of training applications, the manually assigned quality scores indicating whether each training application satisfies a set of criteria, the trained model generates the quality score for the application based on the quality scores assigned to the set of features of the set of training applications, and the generated quality score representing a probability of the application satisfying the set of criteria; ranking for presentation to a user of the online system, content provided by the application in relation to other content of the online system based on the generated quality score; and presenting the content provided by the application to the user of the online system according to the ranking.
9. A computer program product comprising a non-transitory computer-readable storage medium containing computer program code for: extracting features from an application linked to an online system, the application used by users of the online system and configured to post content to the online system, the application operating independently of and external to the online system; applying a trained model to the extracted features of the application to generate a quality score for the application, the trained model is trained by identifying features extracted from a set of training applications, quality scores are manually assigned to each of the set of training applications, the manually assigned quality scores indicating whether each training application satisfies a set of criteria, the trained model generates the quality score for the application based on the quality scores assigned to the set of features of the set of training applications, and the generated quality score representing a probability of the application satisfying the set of criteria; ranking for presentation to a user of the online system, content provided by the application in relation to other content of the online system based on the generated quality score; and presenting the content provided by the application to the user of the online system according to the ranking. 10. The computer program product of claim 9 , wherein ranking the content provided by the application in relation to other content of the online system comprises: generating a quality score for each of a plurality of other applications linked to the online system; and ranking the content provided by the application in relation to content provided by the plurality of other applications based on the quality score of the application and the quality scores of each of the plurality of other applications.