Something very interesting was seized last month is Louisiana, A DIY Integrally suppressed PCC, the Partisan-9. Seized a result of a guy threatening another driver on the road with a "3D Printed gun" (unknown if the Partisan-9 itself). Very curious occurrence, and based on the presence of filament in the seizure pic AND the presence of an unnecessarily tacky pistol grip I believe this example was self manufactured by the guy himself. Which means that we live in an era in which any road raging retard can build himself an Integrally suppressed PCC.

Staying on the topic of 3D Printing, Prominent Developer Ivan The Troll has showcased his latest innovation, the PM-1 fire control group, AR compatible, Trigger, Hammer and disconnector are printable, everything else is COTS. All in all this design renders his previous design (The Common Sense Gun Control Group) obsolete for DIY Purposes.
He has also uploaded a youtube video giving a broader overview of the project
Desert Eagle in the PPKDW/3011 Style via a Printed frame, expect inevetable buffer tube and pic rail adapter abominations. Designed by Pembleton & Sons. And yes it works
A guy is working on Printing a thompson receiver and has made it compatible with an AR FCG, and thus Hoffman Super Safeties (regardless of their dubious regulatory approval)

A guy on reddit has been chopping up and screwing together various parts to create this, an unnamed homemade Bufferless long stroke piston system, modeled after the Kel-tec SU-16 (that is where the gas block is sourced but a DIY one is being worked on). The Tube above the barrel houses the piston and the recoil spring is nested over it. Guy is working on creating a custom upper for it. Even has vague ideas for modifiying the design to make a downward ejecting bullpup rifle
Mosin that has been converted to 8.6 Blackout by Sovereign Development
Before they had their EZ Tune gas tubes, Black River Tactical had their Micro Tune gas blocks. Users would tune their gas system through threaded inserts with center drilled bores of various sizes, essentially allowing the user to have a gas port as big or as small as they wanted (within the physical limitations of the "master" hole drilled and threaded to accept the various inserts of course). This design was essentially the same as the gas jet system that SCAR's use.

I bring this up because I found a thread by a guy detailing how he made his own at home version of this system with simple hand tools. An archive of which can be found below
Doesn't matter how worn your gas port gets if you can just add a second gas port that is much smaller
Comped Alien, it is only proper that a pistol with such features and design elements should have every possible add on to further increase its performance
"Arhipov's Lever" AK mag release
One of the guys working on the 3D Printed Bizon mag for KP9/AKV style guns is as a side project making a Glock Compatible version

Requires a proprietary cartridge elevator that can only be made by DMLS 3D Printing, so probably not DIYable for most people
Ridgeline Defense (they are from what I understand, THE people to go to for training on 5.56 SPR type rifles) have recently come out with their RD-15 LPR rifle. It is a proprietary SPR type rifle that meets all of their exacting specifications. The rifle has an extended barrel journal which the handguard directly mounts to instead of a barrel nut (which in the case of the LPR is tasked solely with retaining the barrel). Said handguard has an integrated Arca rail. The barrel is a proprietary profile 416r Stainless Proof Research 16''. Ridgeline has the club of jam nut retained gas blocks (KAC, Q and Barrett) with the LPR.
A user on /r/NFA has released an updated version of his Suppressor Failure tracker. So you don't feel stupid like I did, to swap between the totals and the failure report section you have to click on the little tabs at the bottom of the page