Main is a mutable conception, but I answered on the criterion of most use, and that still means at least two iMacs, but realistically includes a 9600 and a third iMac. A PB 1400/G3/400 does very nicely for travel, and can still (barely) creak its way through some of the more demanding websites over dial-up. In a sort of order, the active Macs are:

Indigo iMac/500 (8/2001) OS 10.4.9 (business, Web, research)
Snow iMac/500 (7/2000) OS 10.3.9 (Web, software experiments)
Indigo iMac/500 (3/2002) OS 10.2.8 (wave editing)
9600/G3/400 OS 9.1 (server to all 68K/60x Macs)
Beige G3/400 MT OS 9.2.2
Beige G3/400 DT OS 9.2.2 (wave editing)
7300/G3/400 OS 9.1
Quadra 950 OS 8.1
Quadra 700 OS 8.1
Quadra 605 OS 8.1
Colour Classics OSs 7.6.1, 7.5.5, 7.5 (IIe emulator), 7.5
IIci/50 System 7.6.1, 7.5.5
SE/30s System 7.5.5, 7.5
Classic IIs System 7.5.5, 7.5
512Ke System 6.0.8

There are several 60x Macs in the course of resuscitation/upgrade, and some resting, as well as a heap of 68K/60x PowerBooks (160 to 1400/400). Most of the older Macs are getting at least sporadic attention, but to list all would be otiose.

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(60x) 13DT + 3PB + PTPro; (G3) 7DT/MT; (G4) 3T + PB. System 8.1 to OS 10.5.8