"roaming" in 802.11 - yes, a very few vendors have something in a few of their high end products in consumer gear.
I doubt there's any real cross-vendor interoperability (but that's never concerned Apple!)
The managed AP commercial WiFi (Aruba, Cisco, others) have controller-directed handoff. That's like cellular's base station directed handoff.
Better is the client device initiated handoff - usually with a neighbor-AP list broadcast by each AP's beacon. No controller needed. But AP's must discover each neighbor and then collaborate (AP including the AP within a WiFi router).
And the client must be specific to what those APs send to advertise the network topology.
Vocera uses fast handoff - as a WiFi VoIP device, they have to use commercial quality APs with fast handoff, to include the hardest part: securly passing the encryption credentials for TCP-SSL/TLS/VPN connections so that doesn't have to be reconstructed at the expense of the user experience. Then too, there's the issue of 802.11 WEP/WPA keys which can differ by AP, same SSID, but usually don't, and can vary by SSID choice, etc. These security issues are the hard part of roaming.
If only 802.11/WiFi had done layer 3 encryption, and not at layer 2 with WEP/WPA, this would all be so much easier.