DualCAD is described as 'Microstation DGN alternative - opens a V8 file, V7, a raster CIT file and a hybrid raster file of the moon. Runs completely standalone, does not use or require Microstation or OpenDesign to be installed on the client machine'. There are five alternatives to DualCAD for a variety of platforms, including Windows, Linux, Online / Web-based, Mac and PortableApps.com. The best alternative is LibreCAD, which is both free and Open Source. Other great apps like DualCAD are MicroStation (Paid), NttCAD (Free), Piglet Drawing Editor (Free, Open Source) and Dock Designer (Paid).
LibreCAD (originally QCad then CADuntu) is an open source 2D CAD application for Windows, Apple and Linux. It is based on Qt, which is a leading cross-platform application and UI development framework.
NttCAD: free, simple 2D/3D CAD software, multi-platform (works on Windows, Mac, linux...). Programmable in Java language. Small program size and fast download. Saves in autocad dxf, svg and NttCAD formats.
2-D engineering drawing editor that supports hierarchical object description. It is inspired by Hewlett-Packard's proprietary HP PIGLET (Personal Interactive Graphic Layout EdiTor), which later became the commercial Graffy editor by DURST CAD.
Customized to the specific building rules of dock building companies, Dock Designer enables visual design in 2D where you can see your dock design in 3D and have instant access to accurate estimates, parts lists, blueprints, and much more.