Options include Microsoft's own Remote Desktop Connection Client for Mac, the open-source project CoRD, and iTap Mobile RDP. I use the iTap application since in my experience it has much better performance, but it's not free. You can also install VNC on the Win server and use Apple Remote Desktop, the subject of this forum, but one of the applications that use Microsoft's remote connection protocol will perform better and not require additional software ont he server.
Are there possibilities to connect to win ser 2008r2 from a apple platform
In addition to the answer already given, it's worth noting that Microsoft's RDC v2.1.1 (current downloadable version) will not successfully connect to a 2008 R2 server that is running TS CALs due to a license processing bug in that and earlier versions. So, while RDC is free, it's not without its issues.
this is RDP from Microsoft for what you need:
it works with all Windows Servers and Windows PCs which are properly configured.
Unless you fall under the exception which Trane mentioned.
And if there are TS/RD CALs involved on the server, go here:
Search for string "RESOLVED!" on the page and grab the leaked RDC 2.1.2. It solved the CALs issue for me.