What would you do if you'd made £400m in the last tech boom? Relax and take it easy?
Well, for Mark Shuttleworth, the choice was easy, writes Ben King. After a quick trip to space as an amateur cosmonaut, he went back into computing.
But his choice of projects has been a fascinating one. He launched his own desktop operating system. So instead of a Windows computer or a Mac, you can run your machine on Ubuntu.
Even with those deep pockets, taking on tech industry titans like Microsoft and Apple will be tough. But Shuttleworth is giving his product away for free.
Ubuntu will still do all the basic things you'd want a computer to do, like email, web surfing, music or document writing.
For the technologically minded, it has the advantage of being 'open source' - which means you can plug around in the innards and change it or adapt it as much as your technical ability allows. It's less likely to be attacked by a computer virus.
And for some people, the fact that it's not Windows is enough.
It's not the easiest thing to install - it took me about four hours, which I'm told is far above the average, but still too long. And some things just won't work on Ubuntu, notably computer games.
But it's become something of a phenomenon in the computing world. It's the most popular free operating system around, and even the mighty Google has started using it. It's made its own version of Ubuntu, called, naturally, Goobuntu.
Mark Shuttleworth doesn't do many television interviews, but he gave some of his time to More 4 News. Watch the report here.