I don't have time right this minute but I'll give you a full rundown soon.
[Edit] And here it is. WIP to be expanded as I go.
1) Why was SlimDX started?
In 2006, I had a class which required us to do a sizable project in a 'pure OO' language. We wrote a game in C#, using the Managed DirectX 2.0 library. At this time, .NET 2.0 was still relatively recent having been introduced in VS 2005, and MDX 2.0 was still a 'beta' library with 1.1 being the stable branch. It worked well enough though. That spring/summer, it was announced that MDX 2.0 would never become a production library, and the first public previews of XNA were published. (Aside: I was working at Microsoft that summer, and managed to briefly visit with Tom Miller, who mysteriously had an Xbox 360 dev kit in his office. I was asked not to mention it.)
I felt that XNA was technically deficient and filed a couple of early high profile bugs/feature requests. It became clear that I did not see eye to eye with the MS team on how a managed wrapper should look, and I went back to using MDX 2.0. Unfortunately the MS guys had neglected to mention that all of the MDX beta releases were time bombed: you could see in the decompiled source that it checked the current date against a hard coded value and generated an exception, but no one had noticed. So it wasn't just that the beta library was deprecated or not recommended, but that the whole thing literally stopped working overnight. MS refused to release a usable build of MDX, existing code didn't necessarily translate well, and the existing userbase was rightly pissed off.
Remember I'd just written a game? I had a bunch of engine code which was relatively lean and simple in its DX API usage but had some sophisticated tricks that weren't XNA friendly. I figured that it might actually be easier to rewrite MDX than rework the engine. Maybe a week of learning C++/CLI and wrapping work later in December 2006, I had a library that was now source compatible with MDX 2.0, as far as my engine was concerned. I spent the next couple months refining both engine and wrapper to suit my own interests and thought nothing more of it.
Probably some time around March 07, I was discussing the work with a friend of mine, Josh Petrie, who convinced me that people other than me might be interested in seeing and using the library, and signed on to help me out. The name was chosen to sound similar to MDX, while conveying that it was meant to be a simplified minimalist replacement, not a total coverage DX wrapper. I initially published it right here:
That thread has a pretty good run down of what the library looked like at the time, and offers something of a window into my own mindset. It also highlights that I wasn't the first to do this, as Ralf Kormann was working on a (initially) D3D 10 wrapper, which ultimately fell by the wayside. I don't know why. The original source code continues to live on at the beginning of the SVN history:
Check out how many render states were implemented, and how much the Device class was capable of. That was slim. Anyway, Washu joined in to contribute some code within a couple days, and you can see Mike Popoloski's early interest. He eventually starts contributing code in early August, and that's been the core team ever since. You can also see that we start making breaking code changes from MDX almost immediately, and it's a torrent of activity in general.
Aside: In summer 2007 I was working at NVIDIA on the DX9 driver team, which gave me incredible visibility into how the core graphics subsystems actually worked. While not directly relevant to SlimDX work, it did make it clear that worrying about overhead from managed<->unmanaged transitions is pointless. Between working at both MS and NV, I think it helped me build something of a reputation as being uniquely suited to run such a project. That itself is something that still follows me in surprising ways.
2) How was the project organized and managed?
Things needed to get done, people went in and did them. The primary collaboration was and always has been via IRC. Broadly speaking we were working on different subsystems: I was heading up the D3D 9 work, Josh convinced me that D3D 10 should be included and was busy building it, Mike volunteered to deal with the DirectInput code. Washu wrote XInput and was also dealing with math library and architectural stuff, as he had the strongest understanding of the .NET Framework/runtime underpinnings. Later on we'd either use the bug tracker to manage tasks, or just discuss in IRC and do the work.
Ultimately, Mike probably did the heaviest lifting in terms of overall code volume, and dealt with a lot of the really tedious stuff, D3DX in particular. He did a lot of the samples, too. Josh did D3D 10 and I think all of the 11 code. Washu wrote random bits and pieces and addressed a variety of architectural and performance problems. I did D3D 9, D3DX, core library design, developed the main wrapping techniques that we used, etc. I also did documentation, installer, releases, that sort of thing. There were a few other contributors over the years, usually for specific goals.
I would like to note at this point that the site was hosted for many years free of charge by Rim van Wersch, first as a subdomain of mdxinfo.com (which is amazingly still up) and later as its own site. We moved to our own hosting much, much later.