Here is a small list of free plugins that I actually use. I have tried tons of free plugins but this list I actually find myself going to quite often, and some of these find their way into almost every mix or master I do...
Enjoy!
Valhalla Supermassive, Space Modulator and Frequency Echo. These reverb/delay plugins are absolute amazing and fun to use. Ever since I downloaded them I have found almost every project I am using one or more. These also seem to be pretty cpu friendly which is nice for those who used older cpus.
https://valhalladsp.com/
Analog Obsession: These are some of the best sounding eq's, channels, compressors and saturation plugs that I have found that are free. I really can't believe how good they are. The link is to the person I would assume who makes them and you can sign up for donating, but he also lets you download all of them for free as well. I would say probably 7 or 8 of the plugins I use quite often. Highly recommend these:
https://www.patreon.com/analogobsession
Analog Obsession MASBAX which is a mid-side and stereo eq which is very transparent but effective. I find this is really nice when mastering stereo tracks.
https://plugins4free.com/plugin/3222/
Another EQ I use a lot by
analog obsession is the N492ME. Highly recommend this one:
https://plugins4free.com/plugin/3097/
Melda Production: I downloaded these not too long ago and I have just started using them and I have been quite impressed with the ones I have so far used. Their Manalyzer and Msaturator I have used on quite a few project lately, the Saturation plug sounds very good and makes everything sound better just slapping it on. There are probably 20+ free plugins they have, and I have not gotten a chance to use all of them, but definitely a great package of tools to have on hand.
https://www.meldaproduction.com/effects/free
Wiregrind DC offset plug:
I find this is a great very low cpu useage tool if I want to make a quick high pass cut to remove rumble or excess low sub base. I've used it a bunch.
https://plugins4free.com/plugin/2132/
TBProAudio Isol: This is an amazing tool to have on your Mix Bus or Master Faders as an insert. This breaks the frequency up into 5 bands and you can isolate each band for monitoring critical areas with the push of a single button. I love this thing for isolating the low end in stereo tracks when working on kicks and sub bass, or when trying to tame some sharp shrill highs. I definitely recommend this plugin.
https://plugins4free.com/plugin/2871/
Klanghelm DC1A: This is a very nice compressor that I have found myself using quite often for its ease of use and nice warm sound.
https://plugins4free.com/plugin/1681/
VladGSound Molot War Compressor. This thing is awesome! I find that it has quite a bit of capability and is great for coloration and slamming a signal hard.
https://plugins4free.com/plugin/945/
Fuse Audio Labs: Baxandall EQ and saturation. This is a handy plug if you need to just get some warmth in a vocal or instrument but not overdo it. Very subtle yet powerful plugin that I find I use often.
https://plugins4free.com/plugin/3050/
Ignite Amps Pultec PTEq-x: This baby sounds good! I definitely use this one a lot.
https://plugins4free.com/plugin/2468/
Acorn Digital Verbarate Basic: I just downloaded this about a week ago, and I've already used it on 2 different songs lately. Very quick and easy to use and a great sounding verb.
https://plugins4free.com/plugin/3409/
Fuse Audio Labs VREV-666 spring reverb. I downloaded this a few weeks ago and wow, let me say this thing sounds really nice and I find it great to slap on a group bus for light sends from vocals and strings. Very nice sounding.
https://plugins4free.com/plugin/3409/