Metal Gear Ray can NEVER be used in any of the games. There is a short sequence in MGS4 where you can pilot Metal Gear Rex, though.
A Metal Gear is a bipedal nuclear tank which features in most of the Metal Gear games. The first made Metal Gear is Metal Gear Raxa which was known as an ICBMG, then there was Metal Gear TX-55 and Metal Gear D. The next Metal Gears were Metal Gear Rex and Metal Gear Ray. After those they finally perfected the Metal Gears and made what is codenamed Metal Gear Gekko.
Solid snake was looking for Metal Gear RAY.
If you mean story wise then I believe it goes: Metal Gear Solid 3: Snake Eater Metal Gear Metal Gear 2: Solid Snake Metal Gear Solid Metal Gear Solid 2 Metal Gear Solid 4 But I may be wrong, and that isn't counting either of the Portable Ops games.
metal gear solid1, metal gear solid 2 sons of liberty, metal gear solid 3 snake eater, and metal gear solid 4 guns of the patriots.
Metal Gear Solid 4: Guns of the Patriots
There has been no confirmation of a Metal Gear and Metal Gear 2 remake. They are playable on Metal Gear Solid HD Collection in the Metal Gear Solid 3 portion, but thats the only thing that would be considered a remake right now.
Metal Gear Solid, Metal Gear Solid 2: Sons of Liberty and Metal Gear Solid 3: Snake Eater
theres four metal gear solids the first one ends with you and otacon escaping in metal gear ray the seconed ends with raiden defeating solidus who claims to be big boss the third ends with you defeating your mother aka the boss and the fourth ends with you (old snake) blowing up the gw ai and winning the war
the metal wears down from the gear turning metal against metal
Metal Gear Online happened in 2008.
Metal Gear Arcade happened in 2010.
Metal Gear Solid happened in 1998.