(Let me know if this needs to be moved - dg)

xfrog (or “greenworks organic software”): http://www.xfrogdownloads.com/

One of my lsystem attempts in fluxus - a very stylistic approach (all right angles). Trees are built out of cube primitives for an artificial life simulation, in isometric projection:

The cubes approach was too slow (for my old graphics card in 2004) I was spawning hundreds of trees at a time - they were evolving using mutation errors of data encoded in seeds the trees dropped. I later moved to using camera facing geometry (sprites), textured with faked normals to make them shade according to the lighting to appear cylindrical. With a bit of texturing it looked like this:

This worked well (nice and fast) it might be a good technique for background mass foliage - low level of detail for distant plants… I think you can do the face forward calculation in a hardware shader these days.