More open hardware and firmware for sure.
Stuff like Fairphone and Framework are nice steps forward, but those ideals could be expanded to a lot of other electronics, like house appliances.
More open hardware and more community-driven repair hubs would go a long way to help reduce consumer electronics waste and actually help people save money.
But alas, those efforts will always be swimming against a very strong current.
Repairable customizable car platform. Something that could be configured with many features and repowered as technology improves. There’s no reason a well built car couldn’t last 100 years.
A good and customizable app drawer for Android, there are some but most are "minimalist", meaning it's all text, and the other ones don't have the features I want, like being able to organize apps however I want to, not on alphabetical order.
An "file explorer" for images that works with a tagging system.
Something like FilmAffinity or Letterboxd, but federated.
I would like to see a unified and federated approach to the community-driven Wikipedia-like index (list) of information like old-good yellow pages that could compete with search engines. There are "awesome"-lists, ArchLinux list of applications, some Wikipedia lists, etc. All of them are pure gold, but are inoperable with each other and obscure. I would like to see something like a dedicated browser or a webpage showing standardized lists of items with only minimal data: name, description, some types, link to the official website, link to Wikipedia (or whatever).
For example, if I type in "Debian", it shows me that it is a Linux distribution. It is community based, the newest stable version is "11.x". For more information, see "https://debian.org" or "https://en.wikipedia.org/wiki/Debian". Then it offers some related lists, like a "list of Debian-based distributions", etc.
Of course, federation is a necessity if we are talking about the open and diverse web. One server hosts lists of anime & manga, another one hosts a list of cafeterias in a specific region. Plus, in case of failure, these lists could be mirrored by other websites.
I guess, such a project would make the information more accessible, no more filter bubbles. Also, infrastructure costs would be reduced (no need for a crawling and creating snapshots for every single webpage).
Dating software helps you search among a bunch of people those that match your set of filters, and also tells you when you and the other person like each other.
Ideally I would federate between instances and create internally a matrix account for everyone so that communications between matched ones are out of the reach of even the sys admins for privacy.
There is a good non-FOSS app on the play store, Simplemind, which was tracker-free, required no internet connection and also had a healthy privacy policy. Sadly it stopped working because I don't have google play services on my phone and it doesn't let me through the license wall. Smh.