Company making PDP-10 clones.
The F-2 was a small machine. Among other places, it was used at CCMRA (running WAITS) and Symbolics.
The F-3 and F-4 were popular with Tymshare, which built their own versions. Tymeshare's System 26KL was an update of the F-4 design with KL10 capabilities, intended to run Doug Englebart's Augment.
The F-5 was another small machine.