Hello, rajaspoorna.
As far as the Global Menu (the application-specific File, Edit, View, etc menus) go, there is an alpha version of a Global Menu extension for GNOME Shell. You can find out more about it
HERE. Note that it is in Alpha, meaning that it
*could* be very buggy. I have not tested this out myself yet, and it is not fully compatible with all applications at this time.
As far as showing all open windows, the only way I know to do that (right now) is via the Activities Overview. If you simply press the Super (Windows) key, the Activities Overview will open up, and it should be opened to the Windows tab, showing all open windows.
And finally, as concerning custom shortcuts. Here are the steps to take to get to the Shortcuts dialog.
NOTE: By default, for whatever reason, GNOME Shell's Run dialog (which is activated by pressing ALT+F2) is disabled on Ubuntu systems, so there are a few more steps to this than there should be.
- Press the Super key to enter the Activities Overview.
- Type in the following: Gnome Control Center.
- You shoudl see an icon which will launch the Gnome Control Center. Click on it once to open this application.
- In the window that opens, click on the Keyboard item located under the Hardware section.
- Once the Keyboard dialog opens, click on the Shortcuts tab.
Now you can set shortcuts for a great number of things, and you can create custom shortcuts as well. While in tis dialog, be sure to go to the
System category and set a keyboard shortcut (I just used the standard ALT+F2 shortcut) for the entry labeled
Show the run command prompt. this will re-enable the Run command dialog.
I hope that this information has been helpful to you.
Take care.