Good RTree implementation?

(sorry if this is the wrong place to ask this)

I’m looking for a stable, well-tested (and free!) R-Tree implementation. I need to index a lot of line segments to find overlaps, my understanding is that even for one-dimensional range data R-Trees still have performance advantages - or is there a better way to do it?

Thanks for any info; I’d rather not have to do this myself.

http://www.rtreeportal.org/