Okay, I think I know what you're looking for. It appears that GGT is a pretty good solution, as Reed Copsey suggested.
Personally, we rolled our own little library, because we deal with rational points a lot - lots of rational NURBS and Beziers.
It turns out that most 3D graphics libraries do computations with projective points that have no basis in projective math, because that's what gets you the answer you want. We ended up using Grassmann points, which have a solid theoretical underpinning and decreased the number of point types. Grassmann points are basically the same computations people are using now, with the benefit of a robust theory. Most importantly, it makes things clearer in our minds, so we have fewer bugs. Ron Goldman wrote a paper on Grassmann points in computer graphics called "On the Algebraic and Geometric Foundations of Computer Graphics".
Not directly related to your question, but an interesting read.