One project I really enjoyed making was an open-source indoor web map for a museum: https://map.fieldmuseum.org/

(Speaking for myself only. I don't work there anymore.)

I don't know if the map's made people's lives any better, or just a little more annoying, maybe =/ Personally, I would've preferred a regular paper map on the back of a brochure, which can be both much bigger than a phone screen and not require any learned UI interactions. Unfortunately, the powers-that-be stopped using paper maps during COVID (a decision I tried to fight, unsuccessfully). So our visitors could either use this map on their phones or not have one at all. In that sense, I guess it was better than nothing...?

At the time we built this (a few years ago), indoor mapping (as opposed to the typical outdoor street mapping of Google/Apple/OSM/etc.) was a pretty niche area, and the commercial solutions we saw were all some combination of 1) expensive, 2) slow, 3) clunky, 4) too proprietary, or 5) not mobile-friendly.

So we set out to make our own... with a budget of $0 and a dev team of 1 inexperienced web dev (me). It was the first time I ever worked on a web map, and trying to hack indoor areas and multiple floors onto it was... a challenge! It's got a lot of problems (it's laggy on some phones, editing the geometry is a huge PITA, UI isn't great and has bugs, branding/marketing imposed many restrictions, etc.). Honestly, it's pretty jank code that I wish I could rewrite from scratch. We had a whole roadmap of planned improvements and cleanups, but our team was forced to moved on right after initial release.

But on the plus side:

1) It's free and open-source: https://github.com/arcataroger/openlayers_indoor_map (but it's abandoned and I wouldn't recommend using it unless you really have no other options; check https://wiki.openstreetmap.org/wiki/Indoor_Mapping first for alternatives)

2) It uses vanilla JS/HTML/CSS. This is a decision I question in hindsight, as it made state and UI management unnecessarily difficult. But it seemed right at the time, given the need to minimize long-term maintenance (i.e. JS framework churn) because of the limited dev resources available in the museum and nonprofit worlds.

3) It's better than nothing :)

I wish I had the time and resources to rewrite this whole thing from scratch, having learned from this experience. I'd fix a ton of bugs, change up the UI, clarify the symbology, and maybe try to push some of the indoor-specific features as proper upstream PRs to OpenLayers & QGIS rather than just hacking them into this app as one-offs.

I think having a "proper" open-source frontend indoor mapping solution would be a great boon to many museums, art galleries, airports, malls, colleges, etc. Google Maps actually does a pretty good job at this for certain places like airports (e.g. SFO: https://www.google.com/maps/@37.6164644,-122.3859568,17.78z), but their process for that is totally opaque, and it's never clear to me how an institution can ask for their space to be mapped like that (or submit their own?). Even when I worked at the museum, we could never figure out how to actually get their map of us corrected. It's still missing all the floors and many exhibitions are in the wrong places: https://www.google.com/maps/@41.8661273,-87.6169018,20.06z

Maybe I'll pick this up again someday and try to work on it as a side project...