JayneLock is an open source and menu bar based OS X utility that will allow you to launch the screensaver with a click of a button.
If the "Require password..." option on the General sheet of the Security & Privacy preferences pane is enabled, JayneLock will also lock your Mac's screen.
Building from source: Double click the included Xcode project and choose Build from the Build menu in Xcode. This will build the JayneLock application in the "/build/Debug" folder inside the source directory. If using Xcode 4.2 or later you can find the build in the /Users/username/Library/Developer/Xcode/DerivedData folder.
· Apple Xcode (to build from source)