I'll try: hosting solutions, bug trackers, wikis, music sharing, "simple" web-based file sharing, "web operating systems", project management products (incl. to-do lists), anything built on Twitter, anything with "platform" in the name, automated testing tools, blogging systems.
OK, some of these are really meant for technical users (hosting solutions, bug trackers, automated testing tools) but are the companies selling them actually doing badly because of oversupply? Or comparably worse to companies addressing the general public?
It's not a value judgement, just an observation. Clearly there are successful bug trackers.