Creating Classic Goldsrc Based Engine
(aka GoldSrc (https://en.wikipedia.org/wiki/GoldSrc) ).
So, Anyone knows how to get that somewhere and tools for that? Oh, and a few things. Is it possible to modify GoldSrc or Quake Engine ? I Want to make a game like Counter-Strike: Condition Zero or something like that which has some kind of Sandbox or Creative mode.
If anyone knows how to get Quake and GoldSource for free tell me! Skype: swagstorma Steam: CSMakko
That is an obnoxiously large font :)
As for why you want to use the engine, its your own choice - but your time would probably just be better spent using Unity or something similar - I know you mentioned liking old games, but nothing stopping you making an old game in an new engine.
I only did a quick google search, but check out https://developer.valvesoftware.com/wiki/Goldsource at a glance, it appears to have links to what you what
id Software have released all of their classic engine code under the GNU GPL.
Quake: https://github.com/id-Software/Quake
Quake 2: https://github.com/id-Software/Quake-2
Quake 3: https://github.com/id-Software/Quake-III-Arena
Others: https://github.com/id-Software
The game content remains under it's original copyright and licenses. And no, that doesn't mean that you can get the idea that "it's such an old game, no-one will mind" if you redistribute content: they still sell these games on Steam and still make money off them, so they very much will mind.
You can do whatever you like with the code, however, so long as you abide by the GPL.
That doesn't mean that it's the right choice for you. Don't start thinking that just because it's classic and just because it's old it's somehow simpler, because it's not. The Quake toolset is quite awkward compared to what you'll find with a modern engine. The engine itself needs a serious overhaul to work properly on modern hardware. You'll be making a heavy investment in order to solve problems that don't even exist with a more modern game engine. That's cool if that's what you want to do, but maybe you don't; maybe you'd prefer to be spending that time making your game instead?
The engine itself is mostly closed source though -- the core engine is a black box that loads game DLLs created with the GoldSrc SDK.
If you want to modify the engine itself, you'd be better off getting one of the old quake engines, above, which are open source.
There's also no need to use such an ancient game engine though! :P
McGrane posted a link, above, to the valve wiki page, which itself links to a github with the SDK's code: https://github.com/ValveSoftware/halflife
It's also available in steam (under library/tools) as "Half-Life SDK" -- you should probably download this version as it comes with tools such as the Hammer level editor.
You also need to download Half-Life 1 from steam so that you can play your creation.