db4o is an object database for Java and all .NET environments. Its features include ACID transactions, automatic class schema recognition, query-by-example, a S.O.D.A. object querying API, native queries, LINQ support on .NET, callback methods, memory files, cascade-on-delete, multi-threaded access, and Java Webstart and servlet support.
DotNetZip is a zip library for .NET and Silverlight. Using this library, you can build .NET or Silverlight applications that create, view, update, or unpack ZIP archives. DotNetZip also includes a ZLIB library and a BZip2 library. It is all managed code. Compact Framework versions of the libraries are included as well. The ZIP library supports WinZip AES encryption, regular PKZip encryption, Zip64, Unicode filenames, and many other ZIP features.