Screen Recycler 1.3.2 is one option, though not free...
Targeted to all users with two computers to extend screen real estate.
It's like a dual monitor setup without the need to buy an additional monitor.
Use any machine as additional monitor on your Mac.
System requirements:
• Mac OS X 10.4 and/or 10.5 on one Mac
• Two computers, one being a Mac
Price €19.95 + tax
For more information, visit:
http://www.screenrecycler.com/home.html
•••••
{Though I've not tried this, and have no interests in it,
the idea has been around awhile. I'd use the iMac G4
in a location where a computer such as it would be
visible and practical. Since it can play video and do
more than some older entertainment devices. Even
in a near-kitchen area and used to support recipes
and other things while preparing meals may be fine.}
Older Macs had been purposed for tasks including
inventories, garage and small business records, &
other various tasks. The iMac G4 has this great
and striking industrial design, inviting to show it off.
In any event...
Good luck & happy computing! 🙂