what stock adapter is this?

[thatwhichisnt]

Sidefolding as well.

 

[SpeedRacer]

Seen that rifle posted @ M4Carbine.net

The specs are listed as follows:

Krebs Custom AK103k
Aimpoint CompC3 in a modified BP-02 bracket (nice combo but a bit on the heavy side)
ACE Internal Receiver Block
ACE Folding Mechanism with integrated AR15 type Stock interface
Magpul CTR mil-spec stock on cut-down buffer tube (tube Locktite and pinned to ACE adapter)
Magpul AFG on Tapco lower handguard
Tapco SAW grip

Guy's name over there is Canonshooter, I'd shoot him a PM.

 

[spanky]

Yep, looks like an Ace.