A 1-level demo had been released in May 2009 showcasing the then-recent SDL engine and some of its many advantages. A further demo version was released on July 22, 2009 featuring one complete episode and many new guards and atmospheres, all in high resolution.
Music was likewise in high resolution, resulting in it being hosted outside of the Dome. A new palette was also added. The mod conjured up a very unique atmosphere and features a loose theme of DOOM and magic/medieval influences.
A sequel, Project X Insurrection, was announced back in 2010 and after almost 9 years, it was released in its beta form on April 7th, 2019, with no further updates as of now.
The above link directs to the general Project X download page, where each component can be downloaded separately. This comes in handy, as the music itself is more than 200MB (!)