Should ship in July (!). Based on the Nordic nRF52840. $9 for Xenon (BLE+mesh), $15 for Argon (BLE+mesh+wifi(ESP32-S0WD)), $29 for Boron (BLE+mesh+LTE). I like that it has an onboard lithium cell charge circuit.

I ordered a Xenon and Argon to play with.

Shameless referral linkage, if anyone else wants to pre-order: https://particle.io/mesh?referral=MK92YF