Thanks Howdy.Howdy -
That's kind of broad. Perhaps you can narrow it down? Specific things needed....or similar apps you used on previous platforms?
If you are fresh to Macs, sure.....there is the Apple App store. But you can find more diverse, interesting, and alternative options and some useful reviews at MacUpdate.com. Find something you like, and check the linked alternatives at the bottom of each app page.
I was on Windows Platform and now moved to OS X. I am researching on some productivity apps which make my Mac good. First thing I am looking is a password manager as want to migrate all my database to OS X. Earlier I was using KeePass but for Mac it doesn't feel so good.