Bleam scanner is an inverted Bluetooth low energy (BLE) beacon communication protocol. In the inverted communication scheme beacon serves as a scanner, taking this role from a phone that in its turn is responsible for advertising. The main benefit of such a design approach is its ability to function extensively in the background, monitoring RSSI levels. See: https://github.com/Connax-Oy/Bleam-Scanner-2
Regarding Ruuvi, Bleam was just tied to their current Nordic chipsets as nRF52832, also it's able to run on Accent Systems beacons nRF51822 and soon will be on nRF52811
are there any specific ties, or is it all just standard BLE stuff - so should work on any BLE device from any manufacturer?
In theory yes, in practice it's currently ported Nordic Semiconductor hardware nRF52840; nRF52832; nRF51822 and nRF52811 is coming. We'll port it on more hardware with the new protocol versions.