(with apologies to Alexander Shulgin)
kali (this webserver) is a homebrew PC co-located at my workplace and made largely from the hand-me-downs of my home PCs over the years, including the case and PSU from my very first 486 PC, bought from a dodgy outlet in East London in 1993.
At home I currently use a Shuttle XPC SN41G2 for most things, a Mini-ITX box as a firewall / DNS / backup MX etc, and an Atari STe for MIDI sequencing (qv. Music). The first two of these run Debian GNU/Linux, and the last runs TOS and Notator SL).
I have been using GNU/Linux since 1994, starting with kernel 0.99pl15 and the MCC Interim distribution, moving rapidly to Slackware, dabbling with many others and finally settling on Debian. I haven't used any Microsoft products since 2000.
I use a Handspring Treo 600, though frankly not very much as I'm terrified of dropping it. This may be because I'm more used to wielding a Nokia 9000i Communicator (aka The Brick).
These are some of the ageing computers that followed me around for several years but I reluctantly parted with in 2003 to make room for a baby...
My first computer was a Sinclair ZX81, which was bought for my brother in the vain hope that he might do something other than games on it. He didn't, and it was crap for games, so it became mine and I learned BASIC aged 6. Instead of progressing from there to the Spectrum or C64, For a decade I went Acorn with an Electron, a Beeb and then a Master, but eschewed the Arc for a PC in 1993 (the Arc was blatantly a better machine, and RiscOS blatantly better than Windows, it just cost twice as much...)
The largest number of computers I have owned at one time is 10 (acme, sarotti, jimbowen, three Atari STs, three PCs and a broken Sinclair Spectrum.)