I've had a few jams online with random partricipants, real-time, through JamKazam. I was doing it using a WiFi connection to my router until Thursday night when I received an Ethernet cable that I had ordered. WiFi was ok to setup and get used to things, but JamKazam encourages wired Ethernet connections to routers for good reason, using my cable shaved off about ~40ms of latency for me, and put me into a useful latency range for jamming.
Last night I jammed through JamKazam with a few people I had jammed and performed in person with (in person) on a cruise last year, one participant in Tennessee, one in Texas, one in California, plus a couple of other people who I didn't know. I was on mandolin, another person playing bass, and we all observed that if everyone follows the bass carefully, the jam stays much better synchronized. It wasn't perfect, but it was a very pleasant real-time jam experience.
Today we're going to try to get one of our bandmates who lives about 20 minutes away running on JamKazam. We need to get it installed and setup on her laptop, and do it over the phone, so we'll see how it goes. Video is available too with JamKazam, but so far most people I encounter on JamKazam are only using audio (to minimize latency).
JamKazam does also offer a recording tool. I've only played with it casually, but from what I understand the JK servers try to reconcile synchronization issues in a final mix that is completed after the audio recording process is completed. This recording process also includes the ability to have people add tracks in a non-synchronized mode (using a click track).
With using any software tool to have real-time synchronized multi-participant music, personal computer hardware and IP service speed, the number of participants and the distance apart all combine to make up latency. Regarding distance, usually you get about 4.45ms of added latency for every hundred miles, best case scenario. These influences can make the difference between acceptable and unsatisfying real-time synchronized music experiences.
TB/DB thread: Jamkazam - Play with multiple musicians in real time in different locations.