Depends what the things are. And you didn't say (please clarify?) whether this is a user-facing name, or a name seen only by coders. I'm not meaning to diminish

Depends what the things are. And you didn't say (please clarify?) whether this is a user-facing name, or a name seen only by coders. I'm not meaning to diminish the importance of either, btw. For people, it could be a meetup, but others have already offered many better suggestions, such as convergences and serendipities, which both sound good. But maybe you want something shorter. What they do when they get together could also lead to naming ideas. For example, if they connect with each other like modules on the International Space Station, it could be a "dock" event. Your real use case is probably different but you should think about what they do, and what result comes out of their being together, as a source of ideas.