Treu-Structure is a project mainly written in C#, it's free.
3D Structural Modeling and Analysis using Finite Element Method
Treu Structure Copyright (c) 2008 Rafael Forsbach Valle, Claudio Alcerreca Alcocer and Rafael Forsbach Prieto
Parts of this software use dnAnalytics: http://dnanalytics.codeplex.com/ Copyright (c) 2003-2009, dnAnalytics Project All rights reserved.
Parts of this software use ICSharpZipLib: http://www.icsharpcode.net/OpenSource/SharpZipLib/