Quake was released in 1996, but has evolved much since then.
Example Quake Clients Quake
ProQuake // heavily used in multiplayer
Qrack // heavily used in multiplayer
JoeQuake
FitzQuake
Dark Places // very advanced
Tremor
Tenebrae
aRQ-Lite
Quakeworld
FuhQuake // the gold standard Quakeworld client
ZQuake
EZQuake // Carrying on after development of FuhQuake ended
Quake also has several mods. Mods are modifications, usually in the form of Multiplayer games or Single Player Expansion Packs.
Example Quake Mods Quake Multiplayer
Capture The Flag
RuneQuake and derivatives like RQ+ and ZopMod
Rocket Arena
Clan Arena
CRMOD
QuakeWorld
Mega Team Fortress
Quake Single Player
Nehahra
QMatrix
Prydon''s Gate
The Basics
Quake features 8 standard weapons: The rocket launcher, the grenade launcher, lightning gun, the axe, super-nail gun, shotgun, regular nail gun and super shotgun.
You have 100 health and die at 0 health. There are various items like health boxes, armor, ammunition and power-ups like the Quad Damage (deal 4 times damage), the Pentagram of Protection (invulnerable) and the Ring of Invisibility.
Some games feature a grappling hook and some games feature runes. A rune provides a special advantage of some sort such as double damage or regenerating health and armor --- or even the ability to set fire traps, gravity wells or irradiate an area.
Finally some games feature alternate weapons and abilities. IHOC has a jetpack and a flame gun, Rune Quake has bombs and gas grenades, for example.
Mods/Types of Play
There are different types of play, here are a few.
Example Play Types Free-For-All
Everyone against everyone else. All participants are your opponents.
Team Play
Usually the red team versus the blue team. Work together, pack of wolves style.
Capture The Flag
You are blue and your team wants to get the red team''s flag and return it to base.
Cooperative Vs. Monsters
All players are against the monsters only.
Clan Arena+/Rocket Arena
Round based play. Surviving team or player wins the round and scores, then you do it again until a team/player wins.
Runes
Any of the other styles of play combined with runes. Set fire traps, make ice traps, gravity wells, place zombie campers.
Mega Team Fortress (QuakeWorld)
Two teams, different jobs (medics, snipers, and such).
And the above should give you a basic understanding of what Quake is about.