I offered both, but the OSRS server would need alot of time and work to get up and running. Since it's a very very basic framework. On the other hand the RS3 Server is pretty much done in some sections. There is some stuff that needs to be fixed or added, but it's not as much as the osrs server base need's done.
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Edit: You can also make your name color coded like FGunZ is, red for admin, etc, etc. So this can also be handy.