PKzip - way faster and better compression that previous things like ARC. The first version control I did was project01.zip, project02.zip, etc.
SideKick - Being able to pop up and edit underneath a running MS-DOS program was a game changer for me
Turbo Pascal - Being able to compile programs in less than a second in MS-DOS was magic, compared to 15min - hour waiting for the compiler queue on the VAX at school, only to find out you had an error.
Backpack Portable Hard drive - A piece of hardware, but being able to boot a floppy and have 100 megabytes of storage instantly available was like magic.
EDwin - TurboPower Software - the first text editor (that I used) that could record and playback macros, I did all kinds of cool stuff with it.
GoBack - A system tool that kept all the changes to your hard drives.. the salesman demo involved deliberately infecting a system with a virus... then undoing it via GoBack. Unfortunately the wrong people decided it was too slow and "optimized it for speed", which killed the ability to undo virus attacks.
MultiLink - Allowed running of multiple MS-DOS users with serial terminals, usually a Wyse 60.
The $25 network - Allowed the very slow emulation of networking, with just plain old serial ports and cables. Saved hundreds of dollars if you only need a file now and then, back when Arcnet cards were about $100.
Delphi - GUI development for Windows that just works, and like Turbo Pascal, compiles in a blink. Drag your components into a form, hook up the events, make a report or two, and you're done.
Microsoft Office - This one is way under-rated
Microsoft Excel - Reactive programming, comprehensible by humans and accountants.
Microsoft Word - The outliner is quite useful for keeping track of tasks, and the details of projects
Microsoft Access - being able to do a forms based database with nice reports, master/detail records all with zero SQL required is powerful stuff
Microsoft Exchange/Outlook - Exchange is *the world's best database* disguised as a task manager/calendar/email server/client. You can make offline changes, and they just work consistent with expectations.
WebDAV - Uploading by just copying to a folder in explorer was far more intuitive than FTP.
Mercurial - Being able to keep old versions without sucking up the hard drive was very nice.
GIT/GitHub - Being able to keep all versions, branches and push them almost instantly to the web.
Python - The ability to get a lot done in almost no code is very powerful. It's too bad that there's no good GUI for it that works as well as Delphi.
VMware - Ersatz Capability Based Security - The virtual machine gets a set of resources, and nothing more. It'll do until we get better Operating Systems. Being able to save a machine as a file is a very powerful thing.
ThumbsPlus - A photo organizer from Cerious Software, keeps thumbnails in a database, does tagging, etc.
Picassa 3.0 - Killed by google, does local photo management, with local facial recognition, helped me tag the more than 10,000 photos of my daughter. 8)
Hugin - Panorama alignment software - very handy for my experiments in virtual focus/synthetic aperture photography, and for doing landscapes.
GIMP - Orders of magnitude better than Microsoft Paint
WSL - Windows Subsystem for Linux - Allows me to run Ubuntu and Windows programs at the same time. VScode supports running you compiled code in Linux, while it lives in Windows... wizardry!
GNU Radio - If you have a fast enough machine, you can build almost any type of radio you want in a flowgraph, and it supports $25 USB dongles that receive 25-1200 Mhz.