I wrote to Kernighan a few years ago, when "D is for Digital" came out, to ask him, in effect, if troff had been made obsolete by TeX. At the time I had begun using it, and wondered if it was worth investing my time to learn.

He answered that he still preferred to use groff, having tried alternatives. Since then I have used groff exclusively for writing documentation and papers. It never runs out of gas, and always produces attractive output. It offers a complete suite -- math, tables, pictures, graphs -- all in one package. It's fast, adaptable, and easy to learn. It has the highest ratio of text to markup of any typesetting system, including TeX and Markdown. It is the single most overlooked and under appreciated project on the planet.

Whether it's had "significant" development in the past 10 years depends on what that means. Current groff produces PDF format directly, without a Postscript intermediary. The PDF macros support links and TOC generation. I think that all took place in the last few years.