Quake3World

I tried to find some myself, but had no success with Google. I have Audacity, but it's just sound editor as it can't synthetise sound like fire or any animal, or although alien and futuristic sounds than just a noise, a tone or silence track.

I'd make some futuristic sounds myself than finding any throughout the freesound as there are more real recorded sounds than some synthetised futuristic and alien...

Sound recording and synthetising already exist along the mapping as sounds are sometimes part of maps...

I have one sound synthetiser → Cepstral SwiftTalk, but it can only make voice soundfile from a text... I would try making own synthetised sounds just more than voice talking about nothing and also make good stereo music to be used in maps... It will be fully mine and won't break the copyright laws...

There are literally thousands of free sound clips on the web, it take some searching though. I use (or used, until I got stuck in windows 8) Kristal Audio, which is similar to Audacity. They are not 'just' editors, they are pretty powerful multi-track recording apps.
If you can't find what you want you can alter edit the sound, or change to the format Q3 requires.
Quite often I have recorded the sound myself, then edited it into a loop. It's not that hard, workout how to cut and paste and use cross-fade.
Remember to use the right format and frequency for Q3 sounds(which off the top of my head I can't remember). There are plenty of sound file converters that can change file formats outside of the music app. Quite often, if you use free apps, you find you need more than one app to do the job. It takes longer, but once you get a workflow, it is much easier. In most cases, for the hobbyists, there never is a simple answer if we want to create truly unique content.

http://freesound.org

All under CC licenses.

@dONKEY & Eraser:
I know about them, especialy the freesound, but find some suitable sound isn't much easy as somebody can think... Especialy with futuristic sounds they can't be recorded in real life. They must be made by synthetiser, the same is for music loops...

Yeah I know, finding good sounds that fit what you're looking for is hard, and the offerings on freesound or other sites are limited.

Unfortunately I don't know much about creating your own custom sounds.

Macaw (http://macaw.en.malavida.com/) is a free Digital Audio Workstation that supports the VST interface so you can control software synthesizers by sending/recording/editing MIDI commands.
It comes with some synths pre-installed. Their presets are rather shitty though so you'll need to play quite a bit with their parameters.
IMO the program is pretty limited though.

Sony Acid Music Studio is a pretty cheap but much more powerful DAW.

I don't have much practice in sound design but my advice for organic sounds (animals) would be to go with samples. I don't think you can get good results with just synths for those kind of sounds. Wind can be generated with a synth. You'd need a noise generator, modulate that with a flanger or phaser and subtly use a modulated filter.

@Ferrao10:
Okay, have saved the site in my favourites...