I got a Nexus 9 tablet that I'm sharing with my wife.
I set myself as owner and set my wife as another user.
How do I give the other user access to some of the apps I have installed, without re-installing the apps in the other user space?
You reinstall the app, but they use the same install with different data, so the apk isn't downloaded twice (when you click install on a app that is already installed for the other user you will notice it is quite quick). So they already use the same app.
However if you want to share data, you could use one local account, or log in both yours and your wife's local account into the same account for whichever service you wish to share.
I haven't read Android 5 manuals, everything said is just a ~2 hour experimentation since I've opened nexus 7 box and upgraded it to Android 5.
There are several types of users: Owner, Normal, Restricted and Guest.
These observations are incomplete.
If you desire to grant access to applications you installed in your account to your wife, probably best way is to create a restricted account for her, otherwise you may need to pay for some of these apps again.
I just recently ran into this with Android Jelly Bean 4.2.1 and Android Marshmallow 6.0. I found an app called AppShare(+). https://play.google.com/store/apps/details?id=com.spectrl.appshare&hl=en
It does require root, and requires a reboot every time you share apps. There are some ads and there is a restriction on the amount of app-user changes you can make(though I'm not entirely sure how many or how that works?), unless you buy the paid version. It's strengths and limitations are outlined in it's app store description.
I've had some luck with it, and I didn't see it mentioned. It could be a good option in some cases.
Additionally, it can be kind of hard to find in a search, which is another reason I'm posting here.
edit: Recently I've just been doing what ollie299792458 describes.
I was able to share apps on our Nexus tablet, running Android 5.0.2. We have two accounts, mine (as owner) and my wife's. I had installed some apps as owner. Then, when logged in my wife's account, I opened Settings, then Accounts, and added my Google account (so my wife's account has both her Google account and mine registered). I disabled notification/sync for email etc. for my account. Then, I was able to visit the App store and install apps that I had purchased with my account, such as Beautiful Widgets
That's not ideal. All you have to do is turn on sync and you can then read all your emails.
Edit: A solution I've just tested and seems to work is to install your purchased apps on your user. Switch to the other user and add your Google account. Then install again all the apps you wish to share. Once installed for them, remove your Google account. The apps stay and are usable for them.
Google Play's Family Library with app and game sharing goes live July 2, 2016.
From the relevant post on the website Android Police:
Family Library and sharing have been a long, really long, time coming on Google Play. In his different app teardowns, Cody has repeatedly discovered strings pointing out to the feature coming to Play Books, Play Movies, Play Services, the Play Store, but up until recently, the only Google entity that had benefited from any kind of family sharing was Play Music and its Family Plans.
But at this year's Google I/O, Google announced that Family Library was coming to Google Play app and games purchases with the new changes taking effect on July 2nd.
What has already changed though are the terms of the Google Play Developer Distribution Agreement. A new section 5.4 explains how a family group, with one manager and different members, can purchase the product once and share it with other members of the family. So starting July 2, any purchases you make on the Play Store will be available for sharing with your other family members.