Shelly (Allterco) device on my network
Shelly is a Bulgarian smart-home brand, originally from Allterco Robotics and now Shelly Group, known for in-wall Wi-Fi relays.
What Shelly (Allterco) makes
Shelly makes relays that fit behind light switches, smart plugs, dimmers, energy meters, sensors and blind controllers, many built on Espressif chips. Older Shelly devices show up as Espressif rather than Shelly.
What the device on your network probably is
Almost certainly a Shelly relay, plug, dimmer, meter or sensor installed in your home, possibly hidden behind a wall switch by an electrician.
How to work out which device it is
Open the Shelly app or the device's own web page and compare the MAC in device information. The hostname often starts with shelly followed by the model. If you did not install it, it may be behind a light switch or near the fuse box.
Should you be worried
Nothing to worry about: it is a smart-home controller someone installed. If you have recently moved in, it may belong to a previous occupant's setup and is worth resetting.
The app finds every device on the Wi-Fi you are on, at home or in a rental, and puts the vendor next to the hostname, the services it advertises and its open ports, which together usually name the product. Where it cannot tell, it says so instead of guessing. Get RECON for iPhone — one-time purchase, no account, nothing leaves the device.