I present to you VSCO Community Edition, one of the most high quality orchestral libraries that are available out there for free! They've got wind, strings, percussion and brass with articulations to boot! If you want to practice making some big orchestral pieces or to spice up your regular production without throwing out cash on a huge library you may not use, this. is. the. thing!
For a quick overview of what this library can do, let me go over some of the cool features here. They got samples with different articulations for different instruments, all of your staccatos, mutes, attacks, tremolos, vibratos, soft, hard or medium, where applicable. All of it comes packaged in a ton of different variants, .sfz for orchestral samplers (like free sforzando and sfiz), free Ochestools VST3, two different Kontakt libraries, .XRNI for Renoise, and original .wav files if you want to work it into your specific sampler! As a bonus there's a bunch of Omnisphere patches by Man Makes Noise that features movie-trailer and hybrid sounds made from this library!
But if you're trying to pick something for your first time, I suggest going with the .sfz paired with sforzando (Windows and MacOs) or sfiz (Linux). Sfz is a non-proprietary preset format that maps your .wav library to an orchestral sampler. It allows for Key Switch which is a feature for instruments with complex articulation that lets you play different articulations straight from piano roll, no tinkering required! All presets with key-switches built-in are marked with letters "KS", and if you wish to go deeper with it, you can make your own too!
A video-tutorial from Versilian Studios themselves will show you how to set up your .sfz instruments and explain some details related to the format: https://www.youtube.com/watch?v=VomafctByTs
Orchestools is more fit for advanced users that are willing to work with midi mapping, velocity mapping, envelope and LFO modulation to perfect the sound. Mind that you'll have to map every articulation separately so you can use them, as I'm not really aware if there is a Key Switch feature built-in. Also I haven't figured out a good way to work with percussion in it, so it might just not be fit for that use.
All samples are provided with Creative Commons 0 license, which means you can use it for anything you want, commercial production included!