Home (personally): 5 computers
1. 2006 PowerMac G5 2.5Ghz Quad, 16GB ram, 7TB (2 internal drives, 2 drives in USB dock), 6 displays, Leopard OS X 10.5.8
2. 2006 PowerMac G5 2.3Ghz Dual Core, 10GB ram, 2TB (2 internal drives), currently two displays, but video cards for 6 installed, Leopard OS X 10.5.8
3. 2003 17" PowerBook G4, 1.0Ghz, 2GB ram, 120GB HD, Leopard OS X 10.5.8
4. 2006 17" MacBook Pro, 2.18Ghz, 2GB ram, 500GB HD, Snow Leopard OS X 10.6.8
5. 2009 Lenovo Thinkpad L420, 2.5Ghz, 4GB ram, 250GB HD, Windows 7 Pro.
This does not include the other family computers.
Work: 5 computers
1. 2010 MacPro, 2.8Ghz Quad, 3GB ram, 1TB (4 internal drives), 3 displays, Yosemite 10.10.5
2. 1999 PowerMac G4, 350mhz, 192mb ram, 120GB HD, headless, Tiger OS X 10.4.11
3. 1999 PowerMac G4, 400mhz, 256mb ram, 80GB HD, 40GB HD secondary drive, headless, Leopard OS X 10.5.8
4. 2005 PowerMac G5 2.7Ghz Dual Processor, 3.5GB ram, 320GB HD, Leopard OS X 10.5.8
5. 2006 HP Pavillion a1221n 3.06Ghz, 1.5GB ram, 80GB HD, Windows 10 Pro
This does not include the server, which I administrate, nor the other computers in our building.
My PowerPC Macs do not use iMessage, or iCloud (they are too old) so anything I need to sync to all of them or transfer is done via Dropbox (which still works on PowerPC despite Dropbox dropping support). This includes my PC since I am not using iCloud on it. My MBP is also too old to use iMessage and iCloud, so Dropbox works for it as well.
The MacPro at work is not mine so I do not have iCloud/iMessage, etc running on it. Dropbox is installed however. The PowerMac G5 at work is mine so Dropbox is also installed on it.