MP3Tag — does more than what its name suggests, very useful software for tagging music files
Deemix — download stuff from deezer. you will need a Premium account for 320k mp3 and a HiFi account for FLAC.
qobuz-dl — download stuff from qobuz. you will need a paid subscription.
Nicotine+ — modern client for an ancient file sharing protocol. soulseek is surprisingly still active and you can find a lot of stuff there, including in lossless quality
ExactAudioCopy (EAC) — still the gold standard for ripping CDs (what are these, you may ask) on Windows. slow as shit but very reliable. search for XLD and whipper for Mac and Linux alternatives
MKV Toolnix — easily extract, demux, remux video and audio streams
youtube-dl-gui — does exactly what its name suggests
DVD Decrypter — in the (unlikely) case you want to copy a DVD... prehistoric, I know, but there are still lots of interesting movies and concert videos only available on DVD...
Jellyfin — movie/TV library manager and player, free/open source alternative to Plex. I recommend using Jellyfin Media Player as your media player on desktop PC, it works better than through the default web client.
disclaimer: i am not responsible for any actual increase in "productivity" following installation of the following software, please use responsibly.
Everything — search for stuff on your windows PC much faster and with a lot more accuracy than the native windows search. recommend replacing the default search toolbar with the Everything toolbar as well
7-zip — obvious but i still see some people using winrar for some reason... so if you're one of them, install that shit
Powertoys — powerful suite of very useful tools such as Color Picker, Image Resizer and Text Extractor
SyncBackFree — backup automation software
repairing broken stuff
Crystal Disk Info — monitor your hard drives and SSDs for signs of failure. make sure to download the standard edition instead of the bloated anime girl bs
Rufus — create bootable USB keys to reinstall windows/linux on a machine, faster than the microsoft utility
Ninite — multipass installer for common windows apps