Mono 2.0 released
Mono 2.0 is a portable and open source implementation of the .NET framework for Unix, Windows, MacOS and other operating systems.

Microsoft Compatible APIs
- ADO.NET 2.0 API for accessing databases.
- ASP.NET 2.0 API for developing Web-based applications.
- Windows.Forms 2.0 API to create desktop applications.
- System.XML 2.0: An API to manipulate XML documents.
- System.Core: Provides support for the Language Integrated Query (LINQ).
- System.Xml.Linq: Provides a LINQ provider for XML.
- System.Drawing 2.0 API: A portable graphics rendering API.
Mono APIs
- Gtk# 2.12: A binding to the Gtk+ 2.12 and GNOME libraries for creating desktop applications on Linux, Windows and MacOS X.
- Mono.Cecil: A library to manipulate ECMA CLI files (the native format used for executables and libraries).
- Mono.Cairo: A binding to the Cairo Graphics library to produce 2D graphics and render them into a variety of forms (images, windows, postscript and PDF).
- Mono's SQLite support: a library to create and consume databases created with SQLite.
- Mono.Posix: a library to access Linux and Unix specific functionality from your managed application. With both a low-level interface as well as higher level interfaces.
Third Party APIs bundled with Mono
- Extensive support for databases: PostgreSQL, DB2, Oracle, Sybase, SQL server, SQLite and Firebird.
- C5 Generics Library: we are bundling the C5 generics collection class library as part of Mono.
For cross-platform graphics, Mono also offers Mono.Cairo.
For database access, Mono provides bindings to SQLite
If you are looking to manipulate compiled assemblies, Mono.Cecil does just that.