Hello, i have just now tried to run the RTClib.h library 
here is the website i found it on.

here is the code i have copied into Visual Micro:

#include <Wire.h>
#include "RTClib.h"
RTC_DS1307 RTC;

void setup () {
    Serial.begin(9600);
    Wire.begin();
    RTC.begin();
  if (! RTC.isrunning()) {
    Serial.println("RTC is NOT running!");
    // following line sets the RTC to the date & time this sketch was compiled
    RTC.adjust(DateTime(__DATE__, __TIME__));
  }
}
void loop () {
    DateTime now = RTC.now();
    Serial.print(now.year(), DEC);
    Serial.print('/');
    Serial.print(now.month(), DEC);
    Serial.print('/');
    Serial.print(now.day(), DEC);
    Serial.print(' ');
    Serial.print(now.hour(), DEC);
    Serial.print(':');
    Serial.print(now.minute(), DEC);
    Serial.print(':');
    Serial.print(now.second(), DEC);
    Serial.println();
    delay(1000);
} 

here is the error im getting:

Compiling 'test' for 'Arduino Mega ADK'

ccAIeOQc.ltrans1.ltrans.o*: In function main
ccAIeOQc.ltrans1.o*: (.text.startup+0x360): undefined reference to RTC_DS1307::begin()
ccAIeOQc.ltrans1.o*: (.text.startup+0x368): undefined reference to RTC_DS1307::isrunning()

Error linking for board Arduino Mega ADK
ccAIeOQc.ltrans1.o*: (.text.startup+0x388): undefined reference to DateTime::DateTime(char const*, char const*)
Build failed for project 'nexus'
ccAIeOQc.ltrans1.o*: (.text.startup+0x390): undefined reference to RTC_DS1307::adjust(DateTime const&)
ccAIeOQc.ltrans1.o*: (.text.startup+0x394): undefined reference to RTC_DS1307::now()

collect2.exe*: error: ld returned 1 exit status 

Note 1: i have copied the following files from the zip to the project's *.ino directory :

keywords.txt
RTClib.cpp
RTClib.h
 

Note 2: the script works just fine in the normal Arduino IDE

what am i doing wrong?

Thanks for the update. The lib builds okay for me as per zip.

However I note that library folder name does not match a header name in the lib folder. The folder is called RTC the library header is RTCLib.h.

In this scenario both arduino and visual micro have to search and guess what exact library is required. It's possible for an RTClib.h to be located in another library or location so resolving the exact folder is not an exact science. This is why it is important for library developers to follow the rule or a header file matching the folder name.

If in a situation where we go hunting for a library Visual Micro should do the same as arduino so I will take a look however it's very random and best avoided.

Maybe you also have added an RTClib.h to your project and arduino is ignoring it but visual micro is not or vica versa? Difficult to know without seeing your project and other installed libs.

If I recall "RTClib.h" means look locally, <RTClib.h> means use include paths?