There are lots of sites and apps that allow searches with flexible destinations - either a list of specific airports or a general geographic area - but every one I've found recently restricts the search to pure round trips. I'm looking for a site that includes flights into one city returning from a different city (within the specified geographic area or among the specified airports). For instance, coming from New York, if I want to spend a few weeks traveling around Europe, I might start by identifying a few inexpensive pairs of European cities to fly into and fly out of and then, separately, craft a path (via train or short-haul air) to eventually get me from one to the other. If I want to visit multiple cities, I'm better off with an open jaw ticket than a round trip, but none of the sites I've found allow for open jaw searches unless I name the specific airports or cities I'm flying to and from.

In principle, ITA Matrix supports this sort of search - I've done it many times in the past, with long lists of airports - but now it usually errors out, or, when it doesn't, the results it produces are clearly nowhere near the cheapest options. I don't expect Google to fix this, and unfortunately Google Flights doesn't have this capability.

Surely I'm not the only one who would find this useful! Does anything like this exist?