Note: Kontakt instrument is included, picking non-Kontakt orchestra stuff is pretty slim. You can still use the 15 min demo or the "alternative way", if you know what I meant.
ONE - VSCO 2: CE
Samulis, Nimble and @Troisnyx 's creation. Probably the best free orchestra library in the wild. The only public domain and FLOSS library :(
Bonus: Etherealwinds Harp by @Etherealwinds
TWO - Mihai Sorohan Choir
Made by Sorohanro and MaestroRage
THREE - Palette Primary Colors
Pretty awesome Kontakt instrument for orchestra patches.
FIVE - Sonuscore FREE HD ORCHESTRA CHORDS & SUSTAINED STRING CHORDS
SIX - 8Dio Freebies
Err, non commercial, but nobody stopping you ;). Check out the Century Brass and Century String
SEVEN - Ensemblia
Little tool to mess around.
EIGHT - Embertone Ancient Voices, Imitate Strings LITE and Ivory Winds
NINE - Orchestral Rise Builder
TEN - @blackattackbitch SF2 collection
It wouldn't be a complete guide without mentioning BAB collection that helped countless people. His collection is the earliest orchestra stuff that many people, including me, relied on.
Have fun, y'all.
Troisnyx
To clarify, I alpha-tested it, but I didn't produce it. Samulis had a hand in this, but @jiimaan and @camoshark as well. ^_^
zybor
You guys make great instruments!