Thinking that the answer is making something that everyone "needs" to use is a problem. For example "to enter the conference they need to install this app that

Thinking that the answer is making something that everyone "needs" to use is a problem. For example "to enter the conference they need to install this app that also tracks them" is a common thought but it's a bad idea as forcing your end users into a fixed action is bad UX. Mostly it just annoys attendees who will then try and find a workaround. The result of networking apps is some sales people generate a lot of very low quality leads at the expense of the event's reputation as most delegates don't want spam. For messaging apps 99% of messages will be sent by 1% of delegates: the pushy sales people. "Hey, want to meet to discuss my amazing product!" As you say, another option is is "tell me who I was talking to" but again the sales people pollute that experience. B2B events are about selling but there are sales teams who'll scan your badges as they're saying hello (electronically or visually) and then email you forever afterwards. I imagine that "tell me who I stood near" would result in sales teams walking around the entire venue, on the lookup for anyone that looks important to loiter near. Or they could just hide a device in the toilet and get everyone ;) We tried allowing delegates to build a contact list to message and then also notify when those people were at the same networking event just once. It really wasn't much value to anyone other than, you guessed it, pushy sales people that our VIPs would rather have avoided. I don't know if it's still the same but Grip's "tinder for events" used to rely on both parties showing mutual interest before allowing communication. That's the best mechanism that I know of but I wouldn't be surprised if the messaging connection rate was incredibly low.