I can’t believe I can say this, but Sol-T is the most popular and known in this series so far. They are a four membered Hiphop/EDM girl group from Probeat Company who debuted in 2016 with the single Curveball. Their debut line-up consisted of rappers Gyeowool and Chaehee, and vocals Edo and Doa.
Gyeolwool is a former member of coed(?) group Active, who also debuted under Probeat Entertainment, but disbanded after one song.

After Bad Girl promotions, the two vocals left the group and were replaced with two new members: Doori and Jini.

Sol-T has disbanded, however, and the girls, except Gyeowool, will redebut in Probeat's new girlgroup GBB (Rock Paper Scissors). GBB will have two completely new members: Cheris and Sona.

https://www.youtube.com/watch?v=1TvAFCxANRQ (Curveball diamond version)