PreCAD is a 2D CAD application that can be used freely (with advertisements).
You can use many drawing tools without any restrictions.

PreCAD saves files in its own format called "pcad" format, but it supports reading DXF, JWC, JWW (jw_cad) files and writing DXF, JWW files (but there are any unsupported elements, functions, and so on)

You can use the "jws" format of jw_cad as the parts.

In addition to layers, there is a function called "sheet". You can set the scale of "Sheet". By using multiple "sheets", you can mix multiple scales in one drawing.

manual(sorry Japanese only)
https://junkbulk.com/android/PreCAD/manuals/PreCAD_android_manual_jp.html