There are any number of apps that can help you pinpoint a friend's location, but they all have one thing in common: they require that friend to have the same app installed and running, and usually to sign up with YAS (Yet Another Service).
And don't forget, it's a two-way street: you have to run the app yourself, and leave it running all the time -- a pretty big drain on the ol' smartphone battery.
Enter Space-time for iOS, a clever cross-platform locator app that runs only when you need it to and requires no installation or setup from anyone else.
It works like this: you tap Request Someone's Location, then choose a contact from your address book. The app creates a text message to that person, one that includes a brief explanation ("Where are you? Click here so I can see") and a link. If you want, you can tweak the message before sending it.
When the recipient gets the text, all he or she has to do is tap that link and approve a one-time location-services request. Then the person's location is delivered back to you within the Space-time app, where a tap brings it up on a map. It's that simple.
Because this is entirely SMS-based (for the recipient, anyway), there's nothing to be installed, configured, or registered. Plus, the text message should work with any GPS-enabled smartphone, not just iOS-based ones. I tested Space-time with another iPhone and a basic Android phone, and it worked perfectly with both.
I can recall a number of times when I needed to find someone, but couldn't because they weren't linked up with me in Find My Friends, had a non-iOS phone, or didn't want to install a new app. Space-time solves that problem with ease -- and for free. I'm an instant fan.