I'm usually playing a maximum of a handful of games at once, and preferably less. Depending on the games, I can typically handle two or three pretty comfortably. Any more and it becomes a mess. Less is OK, but if I can handle the variety, I don't see why not.

Currently, I'm more or less playing MGS5 and Assassin's Creed: Unity, and it's working out pretty well. It's easy because I've already completed MGS5 earlier and now I'm just doing some extra stuff, so that's just one story mode to go through at once. Now that I think of it, several story modes at once can be a problem, and I tend to avoid it.

Now if we count games I've started but not finished, and which I plan to finish later, the number becomes higher... It probably brings the total closer to ten or even more. Some games relevant in this category include Pillars of Eternity, Far Cry 3, Red Dead Redemption, Gran Turismo 6, and the first Jak and Daxter.

Athe moment im playing a Campaign at Total War Attlia on pc, BF1 on Xbox One and sometimes some Forza Motorsport

Currently I'm going through my back log and playing Batman Arkham Knight as my only story game, but will play BO3 or NHL a bit here and there when my friends are online.

I mainly focus on 1 story game at a time but can juggle between a few multiplayer games as they're just mindless games.

Shadow Hearts (PCSX2)

GTAV Online (PC), mostly racing

Dirt Rally (PC), mostly daily events

Persona 4, Steamworld Dig 2, FF Zodiac Age

Define "simultaneously" and define "play".

Sadly yes.

Tekken 7, Witcher 3 (replay with DLC), Nioh, Dragon Quest 8, Final Fantasy 10, Breath of the Wild.

Those are the main ones that I play right now but there's several others a play a few hours of here and there. I'd like to actually finish games quicker but I get bored playing the same thing for too long.

A few games managed to hold my interest longer than others so I tend to get through those much quicker. Managed to beat Horizon and Yakuza0. My strategy going forward is to just buy less games (already pre-ordered Destiny 2 PC sadly).

Yes.
Nioh
Horizon
Zelda
Ys origins

In the same boat myself. I end up playing a go to game like heroes or Minecraft, while at times trying to continue on with Witcher 3 and Grim Dawn.

gotta chip away. Currently playing, Dragon's Crown, Pokemon Y, Strider (current one), Final Fantasy 15, FF Type-0, Sonic Mania, Titanfall2 (again), Uno, Dragon Quest Heroes, Lego Marvel