I got my OS reinstalled and now all my apps are gone. How do I get them back?

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If you erased the hard drive before reinstalling OS X, that's completely normal. To restore the apps, follow these steps:

1. If you purchased them from the Mac App Store: open the Mac App Store and log in with your Apple ID. Then, go to Purchases tab and download all the apps you had before.

2. If you installed them from a DVD, you'll need an external DVD drive or you can use Remote Disc if you have got another computer.

3. If you got them from an online store, you will have to check that you can redownload them.

A fourth way is to restore a Time Machine backup and get back your apps only. To restore the backup you have to use Migration Assistant (in /Applications/Utilities).

In that case, those apps may be linked to your Apple ID and you may be able to recover them. Try the first way.

Apart from that, it is very important to make backups of your files, so you can get them back in case something goes wrong.

No. Without a backup, there is no place to get them back from.

You are welcome