The best work requires the best tools. But the best tools can only remain that way if proper care is given to them. Without proper maintenance, the sharpest knife soon dulls and your productivity drops.
So here's a few portable tools that are useful for computer software maintenance:
JkDefrag – An open source disk defragmentation tool. Makes use of Windows' own defragment APIs for maximum compatibility. There's a command line version that you can use for scheduling regular defragmentation.
Windirstat – If you ever wondered who's taking up all that hard disk space, this tool comes in real handy. It'll scan the entire hard disk and display folders by space allocation. It even renders a graphical representation to help the more visually inclined quickly find large blocks of allocated space.
Ccleaner – Comes with tools for cleaning out temp files from Windows and a number of popular applications. Ccleaner even has registry cleanup tools.
Auslogic Disk Defrag – JkDefrag works fine but takes rather long to complete. If you're in a hurry, Auslogic Disk Defrag works much faster.
Revo Uninstaller – A lot of uninstallers don't properly clean up after themselves. Often there's a lot of junk left over from an uninstall. Revo uninstaller lets you run the normal uninstall routine and scans for left overs for removal. It doesn't always work as intended though.
Technician's toolbox - malicious software removal tools
How to remove malware from Windows
Bitdefender on Ubuntu