RepRap is a DYI 3D printer with many printed parts. RepStrap is a 3D printer made from convenient to find parts that is tolerable enough to print the right parts for a RepRap. Several people have taken to making minimal RepStraps, it's not a solidified category but people call this type of printer a "JunkStrap" or "RepScrap".
When RepRaps were most popular (around 2012) and RepStrap projects were going crazy, the standard RepRap model was Prusa Mendel where the head (the part from which the hot plastic flows) moved up and down, right and left, and the table on which the hot plastic is placed was responsible for the front and back movement (now less people take up RepStrap projects because you can buy an Ender 3 Pro for under 200EUR (I heard you can buy it for 160USD!)).
Quite popular today among 3D printers which melt and layer plastic are CoreXY printers. The name refers to the way the head is moved, in CoreXY (and a similar setup called Hbot) the head is moved diagonally by two motors and the table is responsible for up and down movement.
My dream is a CoreXY RepStrap, I've heard that through some characteristics of this type of printers they are quite stable and don't need unimaginable precision in making them.
From time to time I take a go e-waste hunting with a friend, one of the best things I found was an old scanner, that scanner had two standard NEMA17 stepper motors (datasheet), this type of motor is standard for 3D printers. I also bought from Ali the absolute minimum hardware to figure out moving the stepper motors (A2560, RAMPS and A4988).
Marlin running on the A2560 is a standard way to run a RepRap, but it will probably be hard for that program to deal with unusual way of moving the head in CoreXY, but I assume that compiling a version with only the features I would need would work (there are forks that support CoreXY).
A 3D printer sadly needs a bit more than good software, power supply, electronics and four motors (I have two additional stepper motors which are not standard NEMA17s), I'm not even sure what parts I'm missing (I know I need at least some screws, some rails, some bearings, relatively long rubber bands, a hotend and some parts to stick it all together). Digging around in the internet I've found some good (I assume so, I didn't dig deeper) CoreXY DYI documentation of RepRap-XY v.2 and Jubilee3d printers but both of them don't work on RepStrap budget and I don't have (for now) skills or experience that would give me hope to finish this project (read: I don't know how to do anything).