The NeuroSky TGAM module is common in toys like the MindFlex game, providing simple proprietary aggregates like "attention" and "meditation" to let players move objects. It's capable of more, and the Arduino Brain library lets you pull the proprietary values and eight separate frequency bands once per second.
I connected one of these modules to three electrodes and an ESP32 + display + battery module from TTGO, and set it up to send updates via either local websockets or an Amazon websocket gateway.
I recorded several data sessions, for things like a "coding trance", a nap, and a full night's sleep. The results are interesting, but until I figure out a proper method for data decimation I'm not going to be able to glean much useful information from it.