Four apps that do the heavy lifting
Every trip needs the same four jobs handled: deciding where you are going as a group, paying for things without falling out, somewhere to sleep, and getting between places. These are what I use for each.
This is the one that fixed group trips for me. Everyone drops ideas, links and dates into one shared plan instead of scattering them across four different chats and a Google Doc nobody opens. The person who normally ends up organising everything stops being a bottleneck, which is the actual problem it solves. I used it to build the Peru route with five people and it held up.
Scan a receipt, split it by item rather than evenly, and it works out the smallest number of transfers to settle everyone up at the end. That last part matters more than it sounds. A two week trip with five people generates sixty-odd expenses in three currencies, and without this you spend the last night with a calculator ruining the mood. Multi-currency handling is the reason I use it over the obvious alternative.
Still the best coverage in Central Asia and South America, which is where the smaller platforms fall down. Filter by map location first and reviews second. In cities like Cusco, Samarkand and Bukhara, staying central removes taxi dependency completely and changes the trip. Free cancellation rates are worth the few extra dollars when your plans are likely to move.
The one I use for flights and for rail in Asia, particularly China where it handles the high speed network properly and most western booking sites do not. Good for comparing routes even when you end up booking direct with the airline. Prices move a lot on the popular regional legs, so check it more than once before committing.