It's called GoKL Bus, now. Only free for Malaysians. Non-Malaysians must pay 1 ringgit.
These are the areas that served by their perspective lines:
GOKL-01 GREEN – Suria KLCC ↺ Bukit Bintang
GOKL-02 PURPLE – Hab Pasar Seni ↺ Bukit Bintang
GOKL-03 RED – Titiwangsa ↺ KL Sentral
GOKL-04 BLUE – Titiwangsa ↺ Bukit Bintang
GOKL-05 ORANGE – Titiwangsa ↺ MINDEF
GOKL-06 PINK – PPR Pantai Ria ↺ LRT Universiti
GOKL-07 TURQUOISE – LRT Dato’ Keramat ↺ Taman Setiawangsa
GOKL-08 MAROON – KTM/MRT Kampung Batu ↺ Chow Kit
GOKL-09 CHOCOLATE – LRT Sri Rampai ↺ Seksyen 10 Wangsa Maju
GOKL-10 PARROT-GREEN – LRT/MRT Maluri ↺ Bandar Sri Permaisuri
GOKL-11 GREY – LRT/MRT Maluri ↺ Bandar Tun Razak
GOKL-12 CREAM – Taman Fadason ↺ MRT Sri Delima
GOKL-13 MAGENTA – MRT Jinjang ↺ MATRADE
GOKL-14 – LRT Muhibbah ↺ PPR Pinggiran Bukit Jalil/Taman OUG
GOKL-15 – Alam Damai ↺ Bandar Tun Razak