We extensively use Ollie O'Brien's OpenOrienteeringMap (oomap) website for informal urban events: https://oomap.co.uk
It's already a fantastic resource and I've been working, with Ollie's knowledge, to add my own improvements. The main ones are:
Global contours (from SRTM - so a bit ropey but better than nothing)
LIDAR-derived contours at 2.5m, 5m or 10m (most of England & Wales, some major population centres in Australia and NZ so far).
Up-to-the-minute mapping data.
Magnetic North grids and map alignment. Also arbitrary rotation (Alt+Shift+Drag)
Downsides: No pre-rendering of O-style maps - only on the PDF and image export. Things take a bit longer as the map data is fetched on the fly. Adding SRTM contours adds a minute or so as the data is only downloaded when needed.
I'm now seeking feedback to see how valuable these additions are. So - please give it a try at the site below. Be aware that this is an ancient PC running off my broadband connection so don't hit it too hard! If feedback is positive I'll work with Ollie to integrate this code into his site.http://oomap.dna-software.co.uk:8888/