OpenStreetMap
I notice Walkhighlands are now using OSM data for the maps on their website. It looks like they are using OS OpenData for roads, placenames, contours etc, plus OSM for paths and tracks.
And the maps look quite nice - fairly similar to an OS Landranger.
See for example one of their walks: http://www.walkhighlands.co.uk/maps/map1_13cg.shtml
They also have a route planner, using the same maps: http://www.walkhighlands.co.uk/maps/
Discussion
Comment from paulatthehug on 5 March 2018 at 18:17
We at The Hug developed that route planner for them. Since then we’ve done a pretty much complete rewrite of the software.
We have also developed our own set of map tiles which we use on various sites again using OSM for a lot of the base data along with OS OpenData for contours, building shapes, and some place names, and other open data sources. We’ve also extended it to cover Eire too.
You can see this all in action on our demonstrator site at https://waymaps.the-hug.net