Apple recently released OS X Yosemite, and it comes with a range of new features one of those is called Handoff, although this feature does not work on some older Macs.
Handoff allows you to easily switch between devices with the same document, web page and more it basically lets you pick up where you left off from one device to another.
Unfortunately this feature does not work on some older Macs, the feature needs Bluetooth 4.0 wot work, and although some older Macs have this, not all of them can support the feature.
Now some developers have come up with a solution to get these Continuity features working on older Macs, and they have released a Continuity Activation Tool, that will enable the feature on older compatible Macs.
The tool can be used to check if you device is compatible, and then it will automatically install the require drivers to enable the features, it will also back up you existing drivers should you want to roll back.
Some older Macs that do not have Bluetooth 4.0 installed may still work using this new tool, although you will need to install a new wireless card to your device, you can find out more information here.