Markus, hopefully you'll take the time to explain how you did it. Of course there's a word-of-mouth factor here, but what other factors are at work here? What else did you do to attract so many players, besides making a good game and putting it on a website?
I have no idea.
Up until about a month ago, I had done no marketing whatsoever. Now recently, I've been doing some google ad words, which brings in about 150 visitors per day. The recent high level of sales started before those ads, though, so I'm not quite sure what triggered it. I might be when 4chan found the game, or just a result of the "indev" (basically like a nightly build, only available to paid members) getting more popular as I've added more features to it, or some combination thereof.
It's pretty interesting. When I started the project, my goal was to focus on making something that's genuinely fun without worrying too much about graphics and stuff like that, and to just be brave and charge for it. I realized that if I wanted to be able to work full time on my own things, they would have to bring in revenue. The original plan was to just work on the game for half a year to a year, but it's starting to look like it's going to last quite a bit longer.
Ideally, I'd avoid feature creep like that, but there's really so much possible in this game, and I can't wait to see how it develops.