Yep I (Ryan from hillmap) am on here. I also follow kaiuhl's went hiking project on github and think its great that he is tackling the social aspects of outdoors sports in an open source way. I may open source hillmap at some point but the code is pretty idiomatic/functional and somewhat optimized javascript and isn't exactly documented or particularly reusable at this point. (My real job is in cancer research...I use hillmap as a place to experiment with things like client side image processing to do slope analysis).

This area (outdoor mapping) is really interesting as there are such segmented user groups. Hillmap's biggest user group is geeky backcountry skiers which generates consistent but not heavy traffic. I've thought about trying to make a comercial go of it but the cost of things like the arcgis layers means it makes more sense to be an ad-free hobby site.

Matt at caltopo has another open source project target at SAR groups and has done some great map layers from usgs and fs scans.