CAPY, the developers of "Below", appear to have confirmed that a lot of what we saw at E3 were timed exclusives.

"Like many games on stage at E3, Below will be available on the Xbox One first. Then, after a period of time, CAPY can bring it elsewhere. It’s always been this way."

Which games could they be? Also, how many is many?

I'll put the guesses here. They have to be games on stage at E3 said to be on Xbox One first. If the developers have commented on exclusivity I'll add links.

Titanfall - "It's definitely not out of the question"

Minecraft - “Microsoft has an exclusivity deal for consoles. When it runs out we’ll consider Minecraft for PlayStation"

Dead Rising 3

Plants vs. Zombies: Garden Warfare

Ryse: Son of Rome

Sunset Overdrive

Crimson Dragon

D4 (Kinect)

Fantasia: Music Evolved (Kinect)

Source: http://www.capybaragames.com/2013/08/pause/

Interesting. It seems like 3rd party exclusives are dying out.

Probably Titanfall and Dead Rising 3, wouldn't hurt if I can get those games eventually.

I'd say Project Spark, not 100$ sure if that's third or first party, if it is third I'd say its timed.

Ryse. But that's only because Crytek will say the millions of sales were below expectations.

titanfall is very likely timed since it is on 360 and PC most likely after the game has been out for a year it will come to PS4 and maybe PS3

Project Spark is 1st party.

Games not Published by MSFT

The first thing to look at is the ones that aren't being published by MSFT like TItanFall, Below, World of Tanks and Garden Warfare, and Fantasia.

Games published by MSFT include 

Dead Rising 3
Sunset Overdrive
Ryse
D4 (I believe)

First Party and Second Party

Killer Instinct
Quantum Break
Crimson Dragon
Halo
Project Spark
Black Tusk Studio
Forza

Dat 15 exclusives.

RIP in piece third party exclusives. I remember when I would fire up a game and it'd be just for that console. Those were the days.

I remember learning multiplats even existed. Man were those the times.