Notepad ++: a quick notepad for all your quick editing needs.
Atom IDE: an IDE-notepad hybrid.
VS Code: after acquisition of GiHub (creator of Atom) by Microsoft (creator of VS Code), it seems Atom won't receive any attention. Moreover, VS Code is working on Live Preview (Google Docs like live document which can be edited in real time!) Which will blow Atom out of the competition even in its current state.
Free Office: a worthy competitor of MS Office.
TeraCopy: a power tool which predicts copy-paste time accurately. It can also perform hash check to ensure your files we copied correctly.
ueli: a simple software which will eliminate the need for Start and dock. Just press Alt+Space and search apps, folders, and settings.
f.lux: reduces blue light from your monitor and helps you maintain your sleeping schedule. Alternative:
LightBulb: suggested by /u/scarystuff
Metatogger: a complete solution for editing MP3tags. Alternative:
Mp3tag: suggested by /u/SparxNet
Todoist: a simple cross platform to-do list app.
PeaZip: a modern zip program which supports almost every compresses file there is. No more annoying trial expired popups.
qBitTorrent: a fast and secure torrent client. Alternative:
Deluge: suggested by /u/ExdigguserPies
BitComet: this is great for both torrents and HTTP (S) downloads. A free and secure alternative to IDM.
MusicBee: a customizeable music application with great tools which won't get in your way.
WinDirStat: get a visual representation of what is hogging space in your drive.
Sumatra PDF: a really small PDF viewer. That's it, its just a PDF viewer for fast loading and no bloat.
PotPlayer: a cleaner, faster alternative to VLC.
youtube-dl: a completely free tool to download audio, video, and playlists from websites like YouTube, Soundcloud, and Vimeo. No more ads, quality limit, first 20 files in a playlist restriction.
darktable: somewhere between stock image viewer and lightroom, and it is non-destructive. Suggested by / u / SparxNet. Alternatives:
Irfan View: suggested by / u / SparxNet.
Photoshop: nothing really comes close to the power and accessibility of PS. Alternatives:
Luminar: great for touch up. Suggested by / u / SparxNet
Affinity Photo: UI stolen inspired from PS. Great functionality for a one time upfront price. Suggested by / u / SparxNet
MS Office: the good old office suite which started it all.
SmallPDF: a tool which converts your pdf to almost every popular format. It is also available for free as a PDF viewer.
BitDefender: after personally trying all the top 5 AV software, this was the most effective while keeping resources in check.
EDIT1: added youtube-dl
EDIT2: added some suggestions from comments
EDIT3: check this comment for some niche and specialized tools.
EDIT4: check this markdown file for some more classified tools aggregated by / u / TheChiefMeat. Fixed a typo.
EDIT5: added vs code