"Package can not be opened because it is from an unidentified developer". Please update the latest version of V2.5 or V2.6.
Apple requires software developers to have Apple approved digital signatures for installation programs to run if your Mac Gatekeeper is on (with Sierra, High Sierra and Mojave the Gatekeeper is on by default). Cadalog, Inc. does has Apple approved digital signature and an active Developer ID. However, during early releases and Beta periods, getting an Apple signature for each new pkg installation file can be time consuming. So we like to wait for a stable release to get the Apple Signature for the pkg installation file. If you do see this message read below. The latest release versions of V2.5 and V2.6 are Apple Signed.
All Mac versions of SU Podium installation (even if they are not Apple signed) can be installed safely and securely for Mac OS-X. Please read below if you are seeing this "Package can not be opened because it is from an unidentified developer" message.
After downloading and unpacking the .zip file, you will see a SU Podium .pkg installation file. Normally you double click on the .pkg file from your Download folder to initiate the install. However, on the Mac OS-X , you may get a similar message as below (for any version of SketchUp):
Currently with High Sierra and Mojave there is only one way bypass this restriction.
Right click on the .pkg file and Open the Installer. See the below image for an example:
When you open the installer, you will see a message like this:
Select open and the installation will begin.