3arthh4ck (Earthhack) is a recode of Phobos. It is considered to be a really good client.
Impact is a very popular client and is considered to be a good alternative to Future Client, a paid one.
Lambda Client is a continuation of Kami Blue, a very popular client among anarchy players.
Catalyst Client was a paid client, but due to it being discontinued, the developers made it open-source.
SalHack is an old 1.12.2 client. The project is discontinued. This is creepy salhack, a continuation of SalHack, which is discontinued too.
Gamesense is a popular 1.12.2 client for anarchy servers. It is discontinued though.
Xulu is a 1.12.2 anarchy client which comes with a lot of modules. It's discontinued though.
Phobos is an unforgettable client. Phobos had an amazing crystal aura but it was ratted by Crystallinq to token log Travis for Wurst+2 (basically watch Wifies' video on it). This is a clean version by GoPro with the removed rat.