available at:
https://web.archive.org/web/20200720134208/http://www.exstora.com:80/download.html

Softpedia has the 2.9 freeware version:
https://www.softpedia.com/get/PORTABLE-SOFTWARE/Office/Calendar-Organizers/Windows-Portable-Applications-Portable-Exstora-Freeware.shtml

404 all over the donwloads page at the official program's site.

I've managed to grab the latest portable version here :
https://download.cnet.com/Exstora-Pro-Portable/3001-2124_4-75305204.html

This is the pro version and seems to be fully functional...

@Midas
I think you may keep instructions for the installer where they were- the download link for the portable version was not easy to find and it may disappear again. ;)

Since there's now a natively portable download for Exstora (see above; thanks smaragdus), I'm moving the executable extractions instructions here:

1. Download the installer and extract to a folder of your choice
2. Delete NSIS].nsi and $PLUGINSDIR
3. Move/copy exstora_dat.xml file from the %APPDATA% Exstora folder into the one with Exstora.exe
4. Launch Exstora.exe

This program seems to be abandoned, but anyway, there is a natively portable build by Exstora developer, I will provide a direct download link for anyone who is interested- http://www.exstora.com/files/2.9/Exstora_2.9_en.zip

I like this little prog and I'm thinking of paying for the extras but, My problem is that I have an event which occurs every 60 days so I have set it up. In 60 days the day is not highlighted even though when you hover the mouse over or click on it the event shows up.

Also. When I went to the web site to report it I fill in the contact form and click submit and it asks me where to save it.

As for making it portable:
I downloaded the 'Exstora_v_2.9_en.exe' file then extracted it using Universal Extractor.
I found the folder '$INSTDIR' and copied the contents to 'ExstoraPortable', (You can use any folder name), and ran 'Exstora.exe'.
This created a bunch of files in, (on my laptop), 'C:\Users\DAVE\AppData\Roaming\Exstora', so I copied the file 'exstora_dat.xml' to the 'ExstoraPortable' folder, then removed the 'Appdata\Roaming\Exstora' folder.

I now have a portable application.

Any application which ignores (or looks shitty with non-default settings) the OS-specific colorscheme, does NOT have an "appealing" and "userfriendly" interface to me - more like the opposite.

Looks like all you need to do to make the app portable is drag the exstora_dat.xml file from "%userprofile%\Application Data\Exstora" folder into the portable directory you are running Exstora from.