Ideas not added:
• FILO Clipboard (First-In Last-Out): A multi-item clipboard holds multiple items and pastes them back out in reverse order. Baked, but not yet popular.
• Speed ahead indicator. Shows the average speed a couple of miles ahead on the motorway give warning and prevent accidents. Already halfbaked though I'm having trouble finding it.
• XML mail storage standard. So that I can archive off my mail and still read the archive when I change my mail application. Looks like the idea's been thought about a lot but not yet completely finalised:
http://www.ietf.org/internet-drafts/draft-klyne-message-xml-00.txt
• Dishwasher dirty/clean indicator (for the avoidance of doubt). A quick google turns up a whole host of these.
• Superscript and subscript numbers — So that you can use powers in plain text. It turns out that these exist in unicode but aren't in a continuous series so they're both difficult to find and often not designed consisitently so they don't fit well together. (?¹²³??????)
• Floating Swimming Pool — a large waterproof bag immersed in the sea or in a river and filled with clean water. Would have been idea for the London Olympics where land is at a premium. The pools could have been created in the Thames with floating grandstands on pontoons for spectators. A quick google tells me that the concept is baked.

[Mar 12 2001, last modified Jun 24 2019]