[0]  C programming  - just pure C on a command line.
[1]  Native OS API calls were used exclusively, which has the additional benefit of creating a hyper-fast program. No .NET / Java runtimes / .dll / plugins / or any other dependencies contaminate the purity that is TinyTask.
[2]  Careful choice of variable data storage size and resource (graphics) optimization for absolute minimum overhead.
[3]  Some interesting proprietary technical strategies, which are trade secrets.
TL;DR   -  TinyTask was programmed with a fanatical obsession for zero code bloat.

I'm just some guy, you know?  Actually, more precisely, some guy who is passionate about efficiency and also happens to be a systems programmer, which resulted in creating TinyTask to do my work for me - and now your work too!  Everybody wins.  :)
So I've now become the programmer who writes your PC automation software for you. It is very gratifying to hear that my little project continues to help people.

There is a single file that is the TinyTask program ("TinyTask.exe") that is the self-contained 32-bit app. The various formats are different ways of packaging the same file.
The "TinyTask.zip" file just contains TinyTask.exe in compressed form, which can be useful for environments where downloading executable files is blocked. Windows can natively extract this file by double-clicking it.
The "TinyTaskSetup.exe" option is a standard Windows installation file. It installs TinyTask to its own Program Files folder and Start Menu app, optionally adds a desktop icon, and also has an uninstall capability. It also includes additional bonus items, such as extra toolbar graphics. This is the typical application package you would get for commercial software. The brilliant Inno Setup was used to create the install package, which TinyTask has supported with donations multiple times.
If you're not sure which one to get, then the Setup option is probably the best choice. Or alternatively the .zip if you want complete control over how the app gets copied and used.

No. This is a false positive.
TinyTask is automation software that records & replays keyboard events (obviously), which causes this app, or your compiled EXE recording, to get incorrectly identified as a keylogger or trojan.
There is nothing malicious in TinyTask code, and a lot of effort has been invested trying to prove this to antivirus companies. The result has been: a) vendors stubbornly refuse to remove the false positive; or b) they remove it, but eventually the flag gets repeated again later.
False alerts have been a constant problem for years, and no more time is going to be wasted on this topic. The future of this project is jeopardized by monopolies like Microsoft and Google that actively block our app. TinyTask does not contain malware, and you can safely ignore scanners/browsers/anti-competitive companies who say otherwise.

TinyTask respects your privacy and includes ZERO spyware or reporting methods.
Our (very brief) Privacy Policy:  Personal information is not shared with any entity for any purpose at any time, ever.
Plus, no personal data of any kind is stored on this web server anyways, so it would be quite challenging to hack (non-existent) information.

Here is the Revision History (changelog)

The license agreement is included with the TinyTaskSetup.exe file and on the software's website. It can be downloaded here: TinyTask-License.rtf

It's a pretty standard software agreement (there might be bugs, please don't steal, businesses are required to purchase, etc). Here is the EULA text:

A flat fee of $495 has been established for revenue-generating businesses with multiple users, which allows unlimited TinyTask installations within a company. Software updates for the current major version are included with this one-time fee. The Business License is required by the EULA.

Upon purchase, a PDF invoice will be issued for a business expense, for tax deduction purposes.
Business funding is very important for TinyTask's continued viability, and special appreciation goes to the companies that have purchased.

TinyTask has been tested on Windows XP, Windows 7, and Windows 10/8.1. It also works well in virtual machines.
TinyTask runs on Linux with Wine (below is a functional test), but compatibility is still being researched.

Listed on the Support page.

TinyTask is developed with a carefully planned feature set, and avoiding feature creep is a serious goal of this software. If you absolutely want to, you can send ideas to [email protected]. Naturally, any request that adds significant size to the program is opposite the TinyTask philosophy and will probably get vetoed.

Actually, yes, many enhancements are planned (and in progress) for this software. I'm usually running a pre-release version as my daily driver. But publicly announcing a release date virtually guarantees that setbacks will happen. It's best to let TinyTask grow organically, like it was originally created.
Encouraging feedback plus contributions are very effective motivators, and help to advance this project. You can directly influence new TinyTask updates.