Ok, so you have made the leap to the world of Linux, but perhaps you still dual boot to run Adobe PhotoShop or some other program due to not knowing if there are equivalent (or near equivalent) programs available under Linux. What can you do?
Well, luckily, there are a variety of ways to kick the Windows habit.
1) Wine - Wine is a Windows compatibility layer, and it runs under Linux. It will allow you to run a variety of Windows programs under Linux. There is an application database you can search to see if your program will work with wine, and how to install it. If your program is not listed, you can still try and install it by running the install.exe (or setup program) with wine. Please submit your experience to the applications database so others may learn from your experience.
2) Linux App Finder - This site categorizes a list of common Windows programs and maps them to equivalent Linux programs. Depending on what features you require/use, the Linux alternative may provide a reasonable functional equivalent. However, for more complex Windows programs and the power user, you may need to experiment with one or more alternatives to get the right mix for you.