I found this interesting Wood Repair Kit at the IWF Show in Atlanta in August. The Danish manufacturer was kind enough to give me their home/DIY kit to try out and review for you. It is very useful. It uses hot-melt elastic material in different colors to fill knots and cracks while remaining flexible enough to resist seasonal movement. It is NOT a glue, but a very useful and easy to use filler. See how it works.
I will add a link soon when it becomes available in the US.