This is a list of notable custom software projects which have significantly failed to achieve some or all of their objectives, either temporarily or permanently, and/or have suffered from significant cost overruns.

Note that failed projects, and projects running over budget, are not necessarily the sole fault of the employees or businesses creating the software. In some cases, problems may be due partly to problems with the purchasing organisation, including poor requirements, over-ambitious requirements, unnecessary requirements, poor contract drafting, poor contract management, poor end-user training, or poor operational management.

Because software, unlike a major civil engineering construction project, is often easy and cheap to change after it has been constructed, a piece of custom software that fails to deliver on its objectives may sometimes be modified over time in such a way that it later succeeds—and/or business processes or end-user mindsets may change to accommodate the software. However, sometimes, for various reasons, neither approach succeeds (or is even tried), and this may be considered as another level of failure—a permanent failure.

Until the significant problems with these projects are resolved, or the projects cancelled, it is not yet possible to classify them into one of the above categories.