I gather ReactOS builds upon the work for WINE and other open-source Windows-compatibility libraries - nothing wrong with that, but it isn't as impressive as it sounds - not that ReactOS as-a-whole isn't impressive as it is.

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Dirty rumour + speculation time: I understand that, to an extent, ReactOS is supported by the Russian government to ensure they have options for running their IT systems in the event of US or NATO-led sanctions which would prohibit service and support from Microsoft corporation. Ordinarily I wouldn't be concerned (geopolitics, yey) but given Putin's current direction... I hope ReactOS is getting suitably security audited...