Pretty sure 4 of those are Linux distros.

Top right is the Ubuntu logo. Top green-yellow one is some African country. Bottom one in blue with three triangles is some fancy hotel brand.

Third row, second column. Tau Empire.

It’s a shame that they aren’t more popular; I didn’t really see prefectural flags flown that much outside of government buildings when I lived in Japan.

My favorites are probably the flags of Niigata and Okayama. They have really appealing colors imo, and the symbols are great as well (especially Niiagata’s).