What word can define an internal solution created within company in contrast to the "external" solutions? Something like "home-made", but more formal and reffering to a company.
As mentioned, "in-house solution" is common and has all the formal and professional meanings that "home-made" does not. "External solution", "commercial solution" or "3rd-party solution" would be the opposites. However, an in-house solution would also clearly say that it isn't immediately compatible with anything else out there.
If you end up numbering things do not, under any circumstances, use the phrase "final solution" - very bad meaning.