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>Apparently you could buy this for $9.95

Sorry, I should have clarified that I was referring to software development. Radio Shack, as a store chain prominently selling kits and Forrest Mims's books on electronics, would have embarrassed itself by not offering schematics for its computer.

What Tandy did not do was offer software documentation. Read this BYTE article from two years after the TRS-80's release (https://archive.org/stream/byte-magazine-1979-08/1979_08_BYT...), which a) discusses how to implement machine language graphics and b) complains about the complete lack of Tandy documentation that motivated the author to write the article in the first place.

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> complete lack of Tandy documentation that motivated the author to write the article in the first place

It looks like Radio Shack published this in 1979: http://www.trs-80.org/trs-80-assembly-language-programming/

It also appears that they supplied a machine language monitor/debugger, T-BUG. So armed with a Z-80 manual and a memory map of the system you could probably do basically anything.

Since the system used block character graphics (like ANSI block graphics), and a memory-mapped display, accessing them from assembly language (or any language) seems like it would be trivial unless they somehow kept the video RAM address and character set a secret.

However, it doesn't look like Radio Shack provided official source listings for their firmware the way IBM (and perhaps other companies) did. I expect that greatly helped with the development of software and tools for the IBM PC, as well as the development of compatible machines.

As much as I like modern computers and smartphones (and systems like the Raspberry Pi) which have absurdly higher speed and greater storage than vintage machines, it's always amazing to consider the explosion of creativity and fun that people managed to have with these pioneering "personal computers."