FOSS Programmer
Discussion page for feasibility of making a from scratch programmer
Existing work: Openprog
mcmaster
While I'm not opposed to such a project, I'm skeptical of the time that it will take to develop such a device and the availability of it vs a COTS solution. In particular, with a TL866 costing $50 and still readily available, effort is much better spent focusing on these.
cr1901
While the TL866 is ending production, the TL866-II is still available/produced. In case TL866-II stops production and both variants become difficult to obtain easily, doing our own design has been proposed before. The short version is we have a lot of good/doable ideas for a FOSS programmer, but it would be a time commitment and would not be as cheap as a TL866. I suspect in principle an open design would attract more contributors in the long run; while Elemecca has done a great job on this front, PIC isn't exactly known to be pleasant to work with.