just look at the online patent record, if you want to get a beginning of an idea about how many of our great ideas are left to collect dust. they are killed intentionally by simply not being used, funded, or paid attention to.

the patent record is a good place to look because patents are not issued to things that cannot be demonstrated to work. i have found list after list of inventions that are all completely explained. if they are more than 17 to 20 years old they are usually listed as "abandoned", which i suppose means you can do with them what you like.