Amazon SimpleDB

I've been a big fan of Amazon's S3 (Simple Storage Service) which is basically an internet-based distributed file system where you pay monthly for storage and bandwidth (separately). I use JungleDisk on top of my S3 account to keep backups of important files like photos, receipts, software licenses, etc.

Now they're releasing a new web service called SimpleDB which is something like a database front-end for S3:

Amazon SimpleDB is a web service for running queries on structured data in real time. This service works in close conjunction with Amazon Simple Storage Service (Amazon S3) and Amazon Elastic Compute Cloud (Amazon EC2), collectively providing the ability to store, process and query data sets in the cloud. These services are designed to make web-scale computing easier and more cost-effective for developers.

Traditionally, this type of functionality has been accomplished with a clustered relational database that requires a sizable upfront investment, brings more complexity than is typically needed, and often requires a DBA to maintain and administer. In contrast, Amazon SimpleDB is easy to use and provides the core functionality of a database - real-time lookup and simple querying of structured data - without the operational complexity. Amazon SimpleDB requires no schema, automatically indexes your data and provides a simple API for storage and access. This eliminates the administrative burden of data modeling, index maintenance, and performance tuning. Developers gain access to this functionality within Amazon's proven computing environment, are able to scale instantly, and pay only for what they use.

Obviously it's not a perfect, end-all be-all system; it uses Erlang instead of SQL, for instance, and you pay for CPU time on top of the bandwidth/storage. However, my experience with S3 was we could pump millions of files into it quickly and safely. So SimpleDB sounds promising not only for small projects, because the cost is almost nil, but also for distributed systems or large amounts of data that require a great deal of speed and redundancy.