OpenDUNE is a source code reconstruction (described as an "open source re-creation", officially) of Dune II that can run natively on modern systems (Windows 32 or 64 bit, Linux, MacOS, and even - not modern at all - Atari TOS). It was created by reverse engineering the original Dune II game executable, making it functionally completely identical to the original game.
The project started in 2009 and reached version 0.9 in 2018-05-25. The game is fully functional.
It requires the .PAK files from the original game, and uses the same graphics and sounds. You need to own the original game separately, so there is no copyright violation. Note that OpenDUNE will also reproduce the anti-piracy check (Dune 2 manual required).
OpenDUNE's aim was to allow playing the original game on modern OSes without emulator, and allow programmers to build on the engine. However, the OpenDune project itself added no updates besides some minor bug fixes.
The Dune Dynasty project expanded on the OpenDUNE code to implement features like multi-unit select, build queueing, construction sidebars, and much more.