The maps subdomain no longer exists, and this site no longer provides map viewers. I am though working on an open-source general map-viewing program; the source is at https://github.com/probins/map-make. The idea is that rather than being something installed on someone else's website, you can easily install it in your own webspace.
There is some documentation, but there is probably plenty of scope for improving this. The software is perfectly usable - I've been using it myself for quite some time - but it's still all rather experimental and still needs more work. So if you can help with either of those, please sign into Github and submit some pull requests.
If you have trouble working out how to install this, please raise an issue on Github.