Building the itinerary is only half the problem with a group trip—the other half is getting everyone to actually RSVP, agree on dates, and pay their share. tfd.golf handles both from the same page.
Once a trip is built, the group gets a shared page to RSVP in or out, vote on dates if they're still flexible, and see a live cost breakdown—split the way golf trips actually work, with green fees charged only to the people playing and everything else split across the whole party. The organizer can attach a Venmo, Zelle, or similar link right on that page to collect deposits, no new payment app required.
Mixed groups are handled too: people flying in from different cities each get their own travel leg in the itinerary, instead of one generic travel day for everyone.