I have developed audiovisual WhiteICE software to alter EEG-metrics (freeware).
It can be (in theory) to increase focus and intelligence but currently software increases synchronization between all brain measurement points and not just midfrontal points at theta frequency as this study does. It supports BrainAccess HALO and Interaxon Muse EEG-devices that don't measure EEG at middle areas of the brain. Research seem to show that mild increase in synchronization between brain regions may increase concentration and intelligence.
You can get about 0.8% change to EEG using audiovisual stimulation using WhiteICE.
Downloads (Windows and Linux): https://www.whiteclinic.net/