The FreeTextBox control provides a WYSIWYG HTML editing environment for ASP.NET (Web Forms) Web pages. Visitors can edit text and click on buttons to format their text. The control is written in C# and has many options for customization.

The .NET Framework lacks support for some network protocols. With Smilla’s .NET Communication Library, developers can add NNTP to their .NET apps. It is written in C# and is distributed under the GNU Lesser General Public License.

MFC classes to add flat, non-3D, “water-color” Office XP-style UI controls to MFC apps. They have no raised edges, do not look “pushed in” when clicked, and are not “shadowed” (except for menus).

Security toolkit with strong encryption and authentication. Supports many algorithms for symmetric/asymmetric encryption, authentication, and hashing. Free for non-commercial/shareware projects. Written in C. ActiveX and C++ wrappers are available.

SourceGrid is a basic .NET grid control. It allows simple data to be displayed without relying on XML. Useful for simple apps, it lacks databinding, WYSIWYG design-time and printer support, as well as grouping and master/detail capabilities.

SharpZipLib is a free, open-source compression library for .NET. It supports Zip, Gzip, Tar, and Bzip2. Also computes checksums. Currently lacks Zip file splitting/spanning, custom self-extracting Zip files, and reading/writing to memory.

Bossware’s SMTPClient is a .NET SMTP client for adding outgoing email to apps and to Web pages. It doesn’t use .NET’s resource-hungry System.Web.Mail, which is merely a wrapper for CDONTS and CDOSYS. Written in 100% managed C# and CLS compliant.