My original 520ST is working 100% Again :)
First pic is with it finally fully assembled *and* fully working :).
This is the first Atari ST my father purchased in 1986 or so, and has been upgraded to 2.5 MB via a Marpet 2MB upgrade. I also added a SidecarTridge TOS emulator, so I can run TOS 1.04 for better GEM drawing routines (and harddisk improvements). This ST came with TOS 1.00 originally.
"Back in the day" we used this to play games, write some C/BASIC software, draw pictures, and then eventually host a BBS -- first on BBS Express ST! then to FoReM ST. (I switched as FoReM handled multiple drive letters for files much better, though I preferred Express overall). My Dad and I wrote a "Trivial Pursuit" BBS door that Keith Ledbetter himself (BBS Express author) later took over (after asking) and improved upon :). I'm also certain this ST was guilty of costing my parents some expensive long distance phone bills...
Last but not least - I have also added a SidecarTridge that plugs into the left side cartridge port to emulate storage devices and more.
EDIT: BBS was named "The DeadBeat BBS", 1986-1994 - 609-853-8084.