Hello stranger. Welcome back.
On the contrary, there's probably more active development going on with GtkRadiant now than there ever was within the same time span. GtkRadiant 1.6 is seeing a lot of changes and development in the last couple of years, what has changed is the needs of the development tools by the community.
First of all, the community is a lot more fragmented, much of the development community branching off to specific mods which are difficult to support individually, and each are using its own branch of the editing tools. GtkRadiant's role in this is to continue to build and support the main code base and allow mod teams to easily fork it for their own projects.
Second is support, it's difficult to maintain the large code base of GtkRadiant when programmers are in short supply and some of the games it used to support are seeing vacant communities. So instead of getting spread too thin, GtkRadiant is focusing on the core games that have programmers to support it as well as a community with demand.
GtkRadiant 1.6 currently supports the following games:
- QuakeLive
- Quake III Arena
- Urban Terror
- Wolfenstein: Enemy Territory
- Quake2/Quake2World
- Return to Castle Wolfenstein
- Star Trek Voyager: Elite Force
- Star Wars Jedi Knight: Jedi Academy
To answer your question though, GtkRadiant 1.4 and 1.5 are both available for download on the website and both support Quake 1. Lookie... someone wrote a little tutorial that I found on Google. Also, Sock has been doing some Q1 SP modding lately, so you can probably poke him with a few questions if you're polite.Quake 1 isn't supported in 1.6 at the moment...
Support for games that were in older release lines of the editor (such as Quake 1), would be pretty easy to add back. They are not included yet because no programmer has made a commitment to support them, and we have committed to "A small subset of well supported games" for 1.6 rather than the old approach of putting in as many game packs as we could.
You will find more details about this in the Mission Statement section of the website.
http://icculus.org/gtkradiant/