You can use multiple FL Studio instances concurrently.
You can then Cut & Paste, Drag & Drop certain types of data (audio, MIDI, etc.) between instances. However, FL Studio also includes various export and file save formats that allow similar functionality (see 'File > Export project bones' in the manual).
Alternatively, you can also run FL Studio inside any VST compatible host. Which means that you can host FL Studio inside of FL Studio. You can find more information regarding this in 'FL Studio as a plugin (VSTi)'.
Note: You may not be able to receive output from additional instances of FL Studio if your soundcard or audio driver do not allow multiple applications to access it at the same time (multi-client). You may use the FL Studio ASIO driver as it is multi-client compatible.
Also, be aware that graphics resources in Windows can be limited (due to compatibility problems). Opening too many instances of FL Studio (which is graphically intensive) could crash your system (although this is less of a problem with modern versions of Windows)!
Image-Line Support Team