Use it to write your novel, while wearing a turtle neck. Find some old Macintosh abandonware and games to run on it. What software does it already have on it?
There's a handful of decent classic Mac games, including the only reasonable version of Dark Castle. Saves you the trouble of emulating it spoilers: there's a lot of trouble in emulating it
I believe the art/sound tools from the leaked Sega Saturn SDK can run on this hardware, that's something you could play with,
I didn't end up keeping it, it looked like it would have been a bother to find old school cables for monitors (2 row VGA, possibly sync issues?) and keyboards/mice (daisy chain PS/2?). I noticed this when I was looking
You can play Bungie's Marathon Trilogy. If you don't mind some of the more dated elements of it, it's a pretty fun shooter with a well written plot for the type of game it is (Doom clone in case you aren't familiar with Marathon). It's legit freeware these days, you can easily download it and a lot of cool user made scenarios legally, put it on some storage medium it can read and play it. Or, forget the Mac and play Aleph One, since despite originally only supporting 2 and 3, it has complete support for 1 now. Also Open GL with hi-res textures and effects.
Bump, whatever, but for the record the keyboards/mice were "ADB" or "Apple Desktop Bus". A proprietary connector used by Apple for low-speed accessories. You definitely could daisy chain them too. Also the monitor socket is Apple's 15-pin RGB but you can adapt that quite easily. At worst you would have needed some kind of sync cleaner to get it to play nice.