MorphOS is a lightweight, highly efficient and flexible media-centric operating system.
SpecsUpdate
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Pros
Pro User-friendly
If you have used and loved Amiga, this is like classic Amiga but more stable and fun to use.
Pro Lightweight
Super lightweight, start up takes less than 20 seconds on 10 year old hardware. Works on most PowerPC-hardware by Apple.
Pro Old Amiga software compatibility
I was surprised to see most of my must have Amiga software worked without problems here like AmIrc, ArtEffect and Personal Paint.
Pro Customizable
You can customize the GUI or download already made parts of GUI from MorphOS storage sites like this one here.
Cons
Con Entirely lacks in security
There's no security at all. All programs share the same memory. The system can easily get hacked, even by a less skilled hacker.
Con Lack of software
Compatible with most modern Amiga software compiled for MorphOS, but does not run modern Windows or MacOS software.