Which program makes Delphi 2010 underline in red wrong codes?

Everton, this feature was introduced from Delphi 2007 if I'm not mistaken. I've never seen it in Delphi 7, but the feature name is Syntax Checker. There are plugins that can help you like CnPack or Delphi Experts.

Update on 8/13/2018

As our colleague @auen mentioned, this functionality already exists in Delphi 2006. In the Code Insight options you can enable and disable Error Insight, which is the plugin responsible for highlighting lines that the IDE thinks are wrong. However, in most cases it makes lines that are healthy, I particularly ignored them (it did not turn off).

I think that because Delphi is a compiled language, often IDE was waiting for a compilation (even in the background) to validate the errors or not. Then the lines were always marked. Even today, this behavior occurs, but less often.

My version of Delphi is 2006 (Turbo Explorer) and it already offers the Code Insight in the IDE.

Among the Code Insight features, Error Insight is what redlights the syntax error locations. But this feature has many bugs (even in newer versions of Delphi) and sometimes indicates errors that do not exist.

If these indications become annoying, simply turn off the Error Insight .

In my version, the path to turn off this option is: Tools - > Options - > Editor Options - > Code Insight . When you reach this window, simply uncheck Error Insight .