Hi, happy to read you.
I try to answer your questions:
- manual: due to chronical lack of time manual are only in italian. I know that some other user are writing manual in some other language. You can try to translate in english the current manual
http://csurvey.it/download/csurvey.pdf even if it is a little obsolete.
- errors: write here some details to allow me to fix it (version you are using v1 or v2, data you are using etc..)
- source code: you can find it here
https://github.com/cepelabs/cSurvey, link is also on cSurvey site. cSurvey use GDI+ and Windows Form (in v2 also directx) (.Net Framework 4.8 ) so there is no linux version.
v2 source code use DevExpress component suite and I cannot share the developer key so, if you download the source code keep this in mind (you can change all from code and you can compile it without limitation).