Evolution in Action
It seemed to me, not too long ago, that most of the obvious web applications, applications I've slowly been using more and more, were already in place and that we had market leaders that were difficult to topple. I'm not talking about Internet Explorer versus Firefox, nor any paid applications, many of these suckers go head-to-head in the free market.
Take forums for example, PHPBB is, from my experience, by far the most widely used forum software. Invision gives it a run for its money, but almost all the forums I use run PHPBB and an overwhelming number of the forums I visit as a result of searches or whatever have likewise been PHPBB boards. It's far from perfect though, big, slow, ugly, it's not easy to adapt it or change the looks and it produces acres of code, most of which is search engine unfriendly and it's not easy to extend. That's not so say there aren't alternatives, such as PunBB, and they seem to be gaining ground. Not so long ago I heard about BBPress, an attempt at a simpler, easier forum by the driving force behind WordPress. It's far from a final release, and isn't as easy as many to install and get working (simply because it's in very early development). I run it on one of my sites and it's a much nicer alternative to PHPBB's bulk. The one that I seem to be hearing the most about at the moment is Vanilla though. It takes a significantly different approach to the forum than many of the others and is much less feature rich as standard, but has the ability to add extensions, so the community can add functionality as it's needed. I installed it recently and it works very well, easy to install, easy to administer (once you get the hang of it) and you can change the look and feel quickly and easily as it has a style/template system. It's still a little on features, but it looks to be developing fast.
These were two markets that I thought were completely dominated with no room for competitors. It just goes to show that you can't sit back and that users will constantly demand improvements. If a new, better product comes along, users will happily jump ship. It also speaks volumes about how much usability and plain old good looks means in the user experience, ignore them at your peril. It also shows how much extensions and customisations can add to a product too.
With this in mind, I'm surprised no one has knocked osCommerce off it's pedestal. It sets the standard for free ecommerce packages, although others are gaining ground. It's a bulky, bloated piece of software which produces horrible code and makes it hard to extend or change the look of (although some of that is due to be addressed in their Milestone 3 release, apparently). As it's open source, I'm very surprised someone hasn't grabbed the code and modified it.
So, just because there are big guns in your chosen market doesn't mean you shouldn't think about entering it, there's always room for a better product.