@zverik@en.osm.town I'd say this isn't even limited to flights but common to all (long distance) travel. Both multi-criteria routing algorithms and UIs for more manual control (e.g. @trans_europe_planner@fosstodon.org) are being looked into to help with that. Cost/availability is currently tricky to consider given the lack of open data. But e.g. optimizing uninterrupted sleep time on night trains could be possible. Either way, the first step is getting the basic schedule data in, all the above builds on top of that.