You can use RootsMagic as your primary genealogy program. It runs on all modern Windows systems, and I have also used it on a Macintosh by using Parallels and also with VirtualBox. If you are not familiar with RootsMagic, you may want to try the free program RootsMagic Essentials first as it, too, lets you share data with the FamilySearch Family Tree. With any of these you can keep your data in RootsMagic. However, you can send whatever segments you select from your database to share with others. (A segment might be one person or all the ancestors of one person—in other words, one branch of your family tree.)
Best of all, you also can find potential new ancestors that are already listed on FamilySearch's Family Tree while you are still using RootsMagic. If you find new ancestors, you can transfer those records directly into RootsMagic in your computer without having to re-type everything.
You can read a lot more about the new capability of RootsMagic in the latest RootsMagic Newsletter at http://goo.gl/KniKp
NOTE: I feel it necessary to insert a warning here. While I am a big fan of collaborative databases available to all, such as FamilySearch's Family Tree, I also have to advise everyone to use these databases with caution. Luckily, that is easy to do.
Never, ever import unverified data directly into your primary database! You need to verify all information first to make sure it is accurate. After all, you wouldn't want to import some other family into your records just because someone else had the same name, would you? Even worse, maybe it is your family, but the person who placed the information online was careless and included many errors. (It happens all too often.)
I would suggest creating a new, temporary database in RootsMagic or whatever program you choose; then you can import all the new records from FamilySearch's Family Tree into that temporary "working database." Spend some time verifying the information for each person in this new, temporary database to make sure each record is correct. When you have verified the information, the process is easy to move or copy each person's information into your primary database. Once you have moved all the verified information into your primary database, you can delete the temporary database.
Unlike many online genealogy databases, FamilySearch's Family Tree allows anyone to add sources and explanations that can help others to verify that the information as accurate. When you import new information, always look at the included source citations. If there are none, you can assume the information is inaccurate. (The phrase "fairy tale" pops to mind.) If the new records include source citations, look at the information referenced to see if you agree. Also, if you already have source citations that are not listed in an individual's record on FamilySearch, you can add the citation(s) to FamilySearch's Family Tree to help benefit others who look at the same records in the future. If we all work together to create VERIFIABLE INFORMATION, we all benefit.
Family Tree has some nifty new features, including the ability to edit and delete most any information about a person, a detailed history of changes made to people, and the ability to add sources to back up your conclusions. I'd suggest you use these new features for your own benefit and for the benefit of others.