Clones
In 1971 to 1972 researchers at Xerox PARC were frustrated by top company management's refusal to let them purchase a PDP-10. Xerox had just bought Scientific Data Systems in 1969, and wanted PARC to use an SDS machine. Instead, a group led by Charles P. Thacker designed and constructed two PDP-10 clone systems named "MAXC" (pronounced "Max", in honour of Max Palevsky, who had sold SDS to Xerox) for their own use. MAXC was also a backronym for Multiple Access Xerox Computer. MAXC ran a modified version of TENEX.
Third-party attempts to sell PDP-10 clones were relatively unsuccessful; see Foonly, Systems Concepts, and XKL.
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