Two things seriously, one in (partial) jest:

A copy utility that can efficiently deduplicate as it copies, even when the filesystem structure is different. Whilst there are many utilities that can deduplicate, they often either rely on files being on the same filesystem, or having the same structure. If a duplicate is detected, it can either be omitted or hard/soft links created to files in one or more reference locations. In practice I have found this to be invaluable for merging and efficiently consolidating multiple hard drives with partial backups of photos and music, maintaining the complete trees of all sources on a single destination, or only copying files that are new.

Secondly, an efficient protocol for text applications over a network. Think a combination of TN3270, SSH and JavaScript, with a very lightweight client/server architecture. Whilst SSH is great, latency kills many practical applications - this attempts to solve that. It also intends to make applications very simple to implement. As a proof of concept, I implemented a simple forum with login, optimistic posting, quoting, a text editor with mouse support in about 600 lines of code. The protocol, client and server themselves are agnostic to any particular UI toolkit.

Thirdly - microfish, poor person's microfiche using laser printers and autoencoders to preserve readability and machine recoverability of high density prints. Since consumer digital archival media seems to be dying...