This computer was an enhanced version of the Challenger IIp. The motherboard was equipped with 3 microprocessors: 6800, 6502A and Z80. An optional 74 MB harddisk was available ($6000 !).
It was supplied with a word processor called WP-1 and a database called DMS. An enhanced version of the operating system allowed to connect up to 16 terminals to the computer at one time.
About OSI, Frank Leonhardt* adds:
Unfortunately OSI did not get its model numbers straight - it was a very disorganised company. A lot of users got the circuit diagrams for bits of OSI equipment and modified one board to another, as they were all made up of the same parts - and dealers would mix and match boards to build a machine to customers requirements.
Their final machine was the Challenger 5, which was a bit like the Challenger 3 but it had five processors - again, OSI could not decide which 16-bit processor was going to WIN so they added a 68000 and a Z8000 to the C3. They never believed that the 8086 would become popular. I know someone connected to their main dealer who saw something about this, but I don't think they were ever sold.
The 74Mb Winchester disk was real - amazing for 1978. Apparently it was very unreliable until the guy who owned it (Dave Graham) covered the outside of the box with lots and lots of fans.
* Frank was the first Technical Editor for the famous Personal Computer World magazine, England's (Europe's) biggest computer magazine - founded in 1978.