I really like Sublime's workspaces system as a solution to this problem.
If you have a project open and need to switch to another one, Ctrl-Alt-P opens the project switcher. If you switch to another project, the previous project's workspace is saved. So when you come back to the last project, everything is JUST as you left it.
Alternatively, if you need to have it open in another window (for comparisons or whatnot), just open a new window before opening the project switcher! (Ctrl-Shift-N, Ctrl-Alt-P)
If you have a project open and need to switch to another one, Ctrl-Alt-P opens the project switcher. If you switch to another project, the previous project's workspace is saved. So when you come back to the last project, everything is JUST as you left it.
Alternatively, if you need to have it open in another window (for comparisons or whatnot), just open a new window before opening the project switcher! (Ctrl-Shift-N, Ctrl-Alt-P)