I'm a lowly PC technician and avid PC gamer. Here's my 'bestof' freeware, I use all of this myself (I'm new so can't post links though, sorry.)
rkill - real time sweep and stop of malicious processes running on your machine. First step in any effective malware sweep/removal.
Malwarebytes Anti-Malware Free - very powerful malware scanner. Untick 'Enable free pro trial' to prevent nagging when the trial runs out and keep free version. Always use Custom scan option and tick 'Scan for rootkits'
HitmanPro Free - Second opinion rootkit scanner.
Cryptoprevent - attempts to secure a system from catching a cryptolocker virus by blocking it writing files to certain folders.
Unchecky - got a family member that keeps installing bundled junk? You need Unchecky! It unchecks boxes during software installs forcing the user to read which selection they want.
AdwCleaner - an anti-malware scanner that targets specifically your browsers and their associated directories. Quick, thorough, requires a restart to complete cleaning. Especially useful for browser hijacks and babylon toolbaresque smuggleware.
Avast Free Antivirus - good detection rates, tiny resource footprint, completely stealth when in Silent/Gaming mode. Does intercept and quarantine incoming exe downloads that it deems very suspicious. Intuitive and snappy GUI.
Adblock Plus/Ublock - block annoying ads, amazingly serene webz can be yours!
Browser extensions
Ghostery - blocks more ads, and trackers, and cookies, and popups
JRT (Junkware Removal Tool) - similar in concept to adwcleaner this roots around in your installs, tells what is possibly dodgy shite letting you decide what you want to remove. Which brings us to...
Proper Uninstallers: There's a few for max coverage.
Revo Uninstaller - the definitive deep uninstaller, performs a standard uninstall then deep scans the system for remaining files, folders and registry hooks then gives you the option to delete them all. Very useful when certain installs go wrong.
IOBit Uninstaller - same deal as Revo but this ones deep scan is not quite as thorough, still great though. Where this app is super important is that it can uninstall 64bit programs, which Revo free can not. Essential tool.
DDU (Display Driver Uninstaller) - excellent tool for completely uninstalling and scrubbing your graphics drivers so you can do a fresh up to date driver install. Can yield boosts to FPS, your mileage may vary
TikiOne SteamCleaner - scans your Steam directories and their dependencies for duplicate runtime installations. Can save you several GB!
Everyone knows CCleaner but for a much more powerful all-in-one cleaner/optimizer look no further than..
Advanced Systemcare by IOBit software - fully configurable to perform: Registry fix, Junk file clean, Privacy sweep, Internet boost, Shortcut fix, Registry defrag, System optimisation, Security audit, Disk Scan, Vulnerability fix (downloads latest windows updates and some others), Disk Optimisation (TRIM/Defrag) - all at once or individually, can set and forget to autorepair, or review the results. Can also set to shut down PC when finished it's work. I've been using this for years and really does keep a windows machine snappy and happy.
On the subject of display drivers
Nvidia Inspector - A powerful driver interface tool which allows you to fine tune how your graphics card handles a particular game. many settings to tweak. Think of it as Nvidia Control Panel ++
RadeonPro - Same deal as above for AMD cards.
MSI Afterburner/RivaTuner et al - idiot proof graphics card overclocking with tons of useful realtime hardware telemetry, should be used in conjunction with...
Furmark - GPU stress testing app, intuitive GUI, many settings, gives the GPU a really good workout so you can watch the temps on that previous overclock

There's a similar tool for CPU overclocking called...
prime95 - batters the CPU like it's Theon Greyjoy, watch those CPU temps on...
HW-Monitor - Monitors and relays via a simple display interface various hardware telemetry, most importantly, temps
memtest86/64 - RAM integrity test
WiNToBootic - Hands down the greatest app for mounting windows install discs onto bootable USB stick.
Yumi - Install multiple linux distros to one USB stick
Hirens Boot CD - Compilations of tools that can be mounted and booted directly from, at start up, to attempt repairs on a broken OS or simply retrieve files from it.
WinDirStat/TreeSize free - see in detail on a graphed interface where and how big files are across all system drives and storage.
NT Password - reset, change and bypass windows password
Borderless Gaming - allows you to go Borderless Windowed in games that don't natively support it.
WSGF - Widescreen gaming fixer - custom resolutions and aspect ratios for many games lacking native support
Reshade/Master Effect Reborn/Sweetfx 2.0 - post processing shader injection, includes FXAA and SMAA, lots of effects, can drastically improve the look of your game with little or no performance hit. I've made a sweetfx profile for IL2 1946, it's the only one on the sweetfx settings database, check it out!
http://sfx.thelazy.net/games/preset/3906/QBittorrent - lightwieght and fast, essential now since utorrent is kill
FRAPS - for me, still the best for high quality screenshots and basic fps monitoring. Lossless video recording is good but badly optimised. For that use...
OBS (Open Broadcaster Software) - many people live streaming on yt and twitch are using this and for good reason, it's encodes in h264(CPU) or Quicksync(Intel iGPU) or NVENC (Nvidia GPU encoding) and is super efficient. You can set it up to record locally at an even higher bitrate too, results in my opinion are stellar if you can push a strong CPU hard with your settings taking care not to harm framerate while capturing. Quality is good cut above Shadowplay and even exceeds FRAPS at times.
MEGAsync - you know you can get 50GB of 'use how you like' cloud storage at MEGA right? Well if you put up large single files or try to download them the browser will struggle and they will eventually fail. The MEGAsync app solves this by creating a folder and using it's own download manager to transfer the file. I found it useful when I put C.U.P. in a single 32GB zip.
CrystalDiskMark - info and benchmarking of your drives
VirtualCloneDrive - simple disc mounting utility
PowerISO/DaemonTools Lite - more feature rich and powerful disc image conversion and mounting
Sandboxie - Quickly and easily run browsers and applications in a sandbox, useful for security reasons
SumatraPDF - reads a bewildering array of mobile text and book formats,lightweight
Teamviewer - remote control application allowing you to fix your moms PC from the far side of the world!
It's late now but if I think of anything else I'll come back.
Hope some of this is useful to someone.
o7