Frogger and Zaxxon were the exceptions in these early years -- most TRS-80 "adaptations" of coin-op games casually ignored minor concerns like proper licensing. But when there was no official alternative -- that is, just about everywhere -- players made do with a number of recognizable, albeit illegitimate, ports.
Before The Cornsoft Group went legit with its Frogger conversion, the company had its greatest success blatantly ripping off Namco and Midway's Pac-Man.
The player's avatar is reduced to a blocky C shape locked into position like a pipe wrench; the five (innovation!) ghosts can't turn blue, so they are forced to shamefacedly cast their eyes downward instead; and the game's chirp-chirp-chirp chomping sound effect is maddening. But it does play like Pac-Man, more or less, especially when using one of the aftermarket Atari joysticks.
Meteor Mission II
"Inspired by" the early Taito classic Lunar Rescue, this Big Five Software effort remains a compelling gameplay experience. The player's tiny pod has to maneuver to the planet's surface through a scrolling asteroid field, rescue a stranded astronaut, then make its way back up to dock with the mother ship. Fuel is limited, and the pod can only fire its puny weapon upward, making the landing very different from the return trip.
Big Five also produced a solid version of Exidy's maze chase Targ, under the title Attack Force, with smart enemies and well-implemented acceleration and deceleration.
This one is a lost classic -- Wayne Westmoreland and Terry Gilman wanted to adapt Nintendo's hit to the TRS-80, and so they went ahead and did so. But Nintendo was unwilling to officially license the game, and so this title went unpublished, languishing in the authors' archives until long after the TRS-80 was commercially dead. While the visuals retain little of Shigeru Miyamoto's cartoon charm -- Mario has no hat or overalls, and his love interest resembles a fire hydrant -- the game is very playable, and just as faithful to the coin-op as the same team's Zaxxon. Like many TRS-80 games, it looks a lot better in motion, with movement helping to distinguish sprites from the background.
Why bother to even invent a sound-alike name, when you can just use the arcade game's title and cross your fingers in case the lawyers show up? Horizon Software's adaptation of Exidy's Venture is so difficult as to be almost unplayable -- for all the wrong reasons. The TRS-80's limited vertical resolution makes the main screen's maze difficult to navigate without getting trapped between encroaching spiders, and if our hero actually manages to enter a room in search of treasure, his shots crawl across the screen, taking one enemy creature out while the others close in to seal his fate.
Crazy Painter (1982)
The whole family could enjoy The Cornsoft Group's Jackson Pollock Simulator... no, wait, that's not right. Does anybody remember one of Williams Electronics' lesser-known coin-op games, Make Trax? Anyone? Well, the Cornsoft Group's Roger Pappas (Frogger) adapted it to the TRS-80 as Crazy Painter. Without the benefit of color and the arcade game's maze structure, the player's paintbrush, the enemies who threaten to destroy the paint job, and the very object of the game vanish into a morass of random pixels.