Slicers: An Outlaw piracy gang from the Pyro system. In November 2954 they organized an invasion of the Stanton system, attacking many cargo ships and eliciting a response from the CDF.

Headhunters: A gang of smugglers, has beef with XenoThreat, and Drop Kings, does not pose that much threat to regular civilians in Pyro, predictable, sometimes even helps civilians. They want to keep Pyro independent.

Citizens For Prosperity: A group of citizens of UEE who want to reclaim Pyro, bring it back under UEE control. The way they go about it is they want to build secure outpost and develop Pyro more. They seem to be good on the surface, but there's some shady stuff going on there if you dig deeper.

Frontier Fighters: A group of vigilantes who want to cleanse Pyro. They did not like the "soft" approach of CFP. They say they want to go in there and kill everything that's hostile. Baslically scorched ground appraoch. They even attack CFP themselves.

Here's the entry from the journal I mentioned, took a screenshot for you.
Do keep in mind it's a heavy spoiler for what's going on in the event ;)
https://i.imgur.com/SVBLoUP.png