Thanks. I didn't say anything because it's hard not to venture into a rant about this huge WTF from nat geo. I get that desktop software is a shrinking market, but it seems like they're 5+ years early with this decision, and it's absolutely puzzling that they didn't develop a suitable online alternative before killing off their desktop product. AllTrails (the subscription site they partnered with) is a social network for hiking, not a topo editor.
Noondueler, this might be a bit much if you don't know what a VM is, but one route is to follow
these instructions to get a copy of XP running on a VM, and then install Topo! on that. If you have a retail copy of Windows 7 (many machines come with "oem" versions that are tied to that machine) you can install it on a free VM like
virtualbox.
Or find a friend that knows about this stuff and get them to do it in exchange for beer.