Details about the project can be found in my blog post: http://volkanpaksoy.com/archive/2015/07/11/rss-feed-generation-with-csharp/
Create a copy of App.config.sample and rename it to App.config. Set the actual values like S3 keys, API keys etc.
To use it offline, build the ArticleFeedGenerator class with OfflineFeedClient and FilePublish Service:
var configFactory = new AppConfigFactory();
var feedFormatterFactory = new FeedFormatterFactory(configFactory.GetFeedSettings());
var apiClient = new OfflineApiClient(configFactory.GetOfflineClientSettings());
var feedService = new FeedService(configFactory.GetFeedServiceSettings());
var publishService = new FilePublishService(configFactory.GetFilePublisherSettings());
var feedGenerator = new ArticleFeedGenerator(apiClient, feedService, publishService, feedFormatterFactory);
feedGenerator.Run();
This way it will read the API response from a given file and save the feed to a local file. Both values must be set in the App.config first.