Will Mainstage 3 run on my 2009 MacBook Pro

I'm running MainStage 3 on OS X 10.11.6. The Minimum System Requirements for MainStage 3 specify OS X 10.11 (El Capitan). I have no knowledge if MainStage 3 runs on OS X 10.10 (Yosemite). You should consider upgrading to OS X 10.11. El Capitan will run on MacBook Pros (Mid/Late 2007 or newer) according to the OS X El Capitan - Technical Specifications web page <https://support.apple.com/kb/sp728>. There is no cost for this upgrade. You can use Google to find many articles that will help you with the upgrade.

You can purchase MainStage 3 from the Mac App Store <https://itunes.apple.com/us/app/mainstage-3/id634159523?mt=12>. When purchased, it will offer the option of downloading an older (compatible) version for your computer. In my case, it downloaded version 3.3.2 even though the current version is 3.4.2.

You have a no cost path to upgrading your computer to El Capitan and a way to purchase a version of MainStage 3 that will run on your upgraded computer. Good luck with the upgrade and enjoy!

I (very recently) installed an earlier version of MainStage 3 (version 3.3.2) from the App Store. This is running on my MacBook Pro (15-inch Early 2008), OS X 10.11.6 (El Capitan). Seems to me working well.

According to the MainStage 3 web page, the Minimum System Requirements are

• 4GB of RAM
• OS X v10.11 or later
• Minimum 6GB of disk space. Up to 51GB of optional content available via in-app download.

https://www.apple.com/mainstage/

I have exhausted my "helpful" suggestions. My situation is different from yours because I already owned MainStage, I just wanted to install it on an older computer. The App Store seems to allow me to download an older version because I already owned the app. This article explains how to download an older app that you already own. <https://support.apple.com/en-us/HT201377>

I'm guessing here, but if you were able to purchase MainStage 3 using a computer running 10.12 (or later), then you should be able to also download an older (compatible) version on your computer. After you own MainStage, you should be able to find the app in the "Purchased" tab on the App Store app on your computer. Of course there are some significant barriers with this approach you (1) need to get access to a computer that will allow you to purchase MainStage (using your Apple ID) and (2) you will be paying for the app before you are sure that this approach will work.

If you can use a friend's computer (running OS X 10.12 or later), this you should be able to open the App Store, sign your friend out of the store and sign-in using your account. Then purchase MainStage 3 and sign-out of the App Store. Go to your computer and download MainStage from the Purchased tab. I'm not sure if this procedure will work so if you want to try it, you should probably test it with a free app with a similar problem.