What type of applications can be developed with AWS SDK for Ruby?

The AWS SDK for Ruby is designed primarily to facilitate the development of applications that interact with AWS services. This includes creating applications that manage AWS resources, automate deployments, and leverage various AWS features, which is effectively what is meant by AWS infrastructure service applications.

Developers can use the SDK to connect Ruby applications to services like Amazon S3 for storage, Amazon EC2 for computing power, or AWS Lambda for serverless applications, among many others. As a result, the SDK provides an extensive set of tools and libraries specifically geared towards managing AWS infrastructure, making this the most fitting choice.

Although the SDK can also be used in web application scenarios since they can interact with backend services hosted on AWS, the most accurate categorization rests within the context of AWS infrastructure service applications, reflecting the SDK's core purpose in enabling developers to work directly with AWS services.