Github Repository, Crowdin Repository
ReactOS is a free and open source operating system written from scratch. It's design is based on Windows in the same way Linux is based on Unix, however ReactOS is not linux. ReactOS looks and feels like Windows, is able to your run Windows software and your Windows drivers, and is familiar for Windows users.
Development began in 1996, as a Windows 95 clone project, and was continued as ReactOS in 1998, with the incremental addition of features of later Windows versions.
As of July 2018, ReactOS is considered alpha software, feature-incomplete but with many Windows applications already working (e.g. Adobe Reader 6.0, OpenOffice, etc) and therefore recommended by the developers only for evaluation and testing purposes.
ReactOS is released under GNU GPLv2 Open Source license, with some parts released under LGPL and BSD licenses.
Sources: Wikipedia/ReactOS & ReactOS Official Website
Subject to 
The project is being translated from English to Greek. I'm a native Greek and because of my job (programmer) English is a "must learn" language.
I worked on: shell32, shimgvw, syssetup, tapiui. There were a few issues with the already translated strings, and I have noted down a couple of strings to show you what I mean.
Let's see what has to be the worst translation in this part:
Setup will create a user account on your computer called Administrator. You can use this account if you need full access to your computer.
the suggested translation by someone else was:
Η εγκατάσταση θα δημιουργήσει ένα λογαριαρισμό διαχειριστή στον υπολογιστή σας με το όνομα Administrator. Με το λογιαριασμό διαχειριστή μπορείτε να αποκτήσετε τον πλήρη έλεγχο του υπολογιστή.
So, what's wrong with it, you may ask... "Account" appears twice in this string, and it was not translated correctly once. Both times wrong:
λογαριαρισμός is like typing accocount and λογιαριασμό is like typing accuount, instead of account. String on Crowdin
There was also a really bad auto-translation, provided by Microsoft Translator:
Check disk options, a really simple string, that could be translated in 2 different ways. Checking the context revealed that it meant "Options for Disk Checks" (context: DIALOGEX['IDD_CHECK_DISK'] -> GROUPBOX['-1']). Microsoft proposed this:
UnderΕλέγξτε τις επιλογές δίσκου
I don't know where this "Under" came from and why it remained untranslated. However the rest of the translation was also wrong, meaning "Check the Disk's Options". The correct translation I suggested is Επιλογές ελέγχου δίσκου.
String on Crowdin
I translated 1184 words, minus an estimated 10% for duplicates and untranslated words, which brings us to ~1065 words, for a total of 30624 words out of 37669 words. All numbers were rounded to the nearest integer (as you obviously can't translate 724.24 words).
CrowdIn project link: https://crowdin.com/project/reactos/
Github project link: https://github.com/reactos/reactos
My CrowdIn profile link: https://crowdin.com/profile/dimitrisp2
My Github profile link: https://github.com/dimitrisp2/
ReactOS is a great project, aiming to help the average Joe try a free alternative operating system, without having to change a lot of his habits. It has a long way to go though, as it is still in alpha development stage. I'm proud to translate this into Greek, as I've always been secretly supporting this project!
I have translated 1184 words (-10% for duplicates and untranslated words = ~1065 words) for a total of 29440 words out of 37669 words. I'm now translating a file used to manage various internet related stuff.
We've been planning since mid-September -if not earlier- to create a community account used as a translation blog, share our knowledge and our stats with everyone. Each one of us could do it from their own account, but having them all concentrated in one place would make it more transparent and targeted. After all, knowledge and tips are best when shared with as many people as possible, but only if they are interested in that.
Our community account, 
Thank you everyone for taking your time to read about my contribution. Big thanks to the 
our ruth-less Language Moderator
and our community account
If you want to support
@katerinaramm
@lordneroo
@trumpman