Software Effects

You made your song and programmed your synths but it still sounds like shit. You also have no way to use hardware effects. Well, here you go.
A quick note on DAW "built-in" effects: Most, if not all of the modern DAWs have audio and MIDI effects bundled with them. While these are usually pretty basic, they can get most of the job done if you don't wanna bother with downloading/buying/torrenting your stuff. It's more about how you use them than what they're capable of, really.
And always remember, if your track sounds whack just SIDECHAIN EVERYTHING.
==Plugin Suites==
===Melda Productions - MFreeEffectsBundle [VST2 VST3 AAX AU - 32 64] - Free===
Melda Productions creates a wide variety of plugins, and this is their free pack. Of course limited in the usability (can't create own presets, sonogram disabled, can't change size and style), and of course not every plugin is really useful or better than the built-in effects of your DAW, this is still worth a look as it contains some useful utilities. You can even buy an upgrade to remove the limitations. The names of the contained plugins are fairly self-explanatory:
: MAnalyzer, MAutopan, MAutoPitch, MBandPass, MComb, MCompressor, MEqualizer, MFlanger, MFreqshifter, MLimiter, MLoudnessAnalyzer, MNoiseGenerator, MNotepad, MOscillator, MPhaser, MRecorder, MRingModulator, MTremolo, MTuner, MStereoExpander, MStereoScope, MUtility, MVibrato, MWaveShaper
==Compressor==
A compressor is used to reduce the dynamic range (difference between low amplitudes and high amplitudes) of an audio signal. The most intended uses for compressors are to make performances more consistent in loudness (for example if a speaker/singer is moving to and from a microphone and therefore sounding quieter or louder), or to make the perceived sound louder.
===Klanghelm DC1A [VST2 VST3 AU RTAS AAX - 32 64] - Free===
Looks and works like a vintage compressor (which also had not a lot of controls), but sounds pretty good.
===vladg Molot [VST2 VST3 AU - 32 64]===
Not a transparent compressor! Adds character and colouring to the signal. The GUI may be scary (and russian) at first, but has some creative potential.
==Limiter==
Limiters are hard/extreme compressors, most often used like a safety net to avoid clipping and distortion. Limiters usually operate above a compression of 10:1. They are often used in the last steps of mastering a track to reach maximum perceived loudness.
===vladg Limiter №6 [VST2 AU - 32 64] - Free===
A free russian limiter, and the default GUI even looks the part (which has its own charm). The general consensus is that its sound quality rivals even very expensive commercial limiters. There are alternate skins available.
==Utilities and Tools==
===Voxengo SPAN [VST2 VST3 AU - 32 64] - Free===
A very useful free spectrum analysis plugin.