General Apps on iPhones and some other smart phones  (Not Maps, Photo and Video apps as they are covered elsewhere)

Find My iPhone (a similar program exists for the Android system involving using the Android device manager web portal.)
This is a great app made even better with the new operating system, #7, released in September 2013. It is the best reason I have seen for upgrading to the new operating system.
It allows you to
1) Find your iPhone or iPad from any computer, Mac, PC or iPad
2) Lock your iPhone or iPad from any computer, Mac, PC or iPad
3) Erase everything on your iPhone or iPad (In the case it is stolen)

The big enhancement with the new operating system is that to disable it, you have to use your Apple ID.  In the past a savvy crook would disable it as soon as he got his hands on your iPhone.

To install it on your iPhone, download it from the Apple App Store, it is free.
To use it from computers other than another iPhone of iPad hat it has been installed on you must set activate your iCloud account from your iPhone or iPad. There is no cost involved unless you store a lot of stuff on it.
To activate it, tap the Settings icon on the Home screen, select iCloud, then enter your Apple ID then scroll down to Find My iPhone and turn it on.
Now to get to it from a browser on any device, Google iCloud.  Then log in with your Apple ID.  Select "Find My iPhone".  It will display the location of your device on a map.  If it turns out it is in your house, you will not get enough detail to tell where so click on the dot representing your device then click or double click on the 'i" with the circle around it and a menu will pop up with options to "Play a sound", "Lost Mode" formerly "Lock my iPhone" or "Erase iPhone"
It will play a distinctive load sound regardless of whether it is on vibrate or not and regardless of the sound level set on it.

You will want to play around with this a little before you really need it as it is a little confusing.

There are some additional benefits if you install iCloud on your PC.  You already have a link to "Find my iPhone" and you can use the iCloud for other things.  The use I found best is to set my iPhone to automatically put a copy of all pictures I take on iCloud where I can get them even if my camera has been stolen as it was on a trip to Paris.  It is a little of a nuisance since you have to delete pictures from the iCloud separately from deleting it from your iPhone.

There is a related program called "Find Friends" which allows you to find friends on the same sort of map display that is used in "Find my iPhone"  A friend can join you temporarily or permanently.  There are obviously privacy concerns but it is handy.  If you told your spouce that you were working late and were actually at a motel on the edge of town, it could give you away unless you left your iPhone at the office of course.

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DocsToGo or Documents to Go  This is a 3rd party version of Microsoft Office that lets you edit Office documents.  It is free unless you want to use it with the cloud or to edit Power Point files in which case it cost $7.99 when I upgraded.  The basic version will sink with your PC but not automatically. 

My next set of instructions assume you have installed DocsToGo with the upgrade, have a Dropbox cloud account and want to save your files there. I also assume you have a printer that supports ePrint or xPrint so you can send a document to print to a specific e-mail and it will print on your printer. Later on I go into more detailed setup options.

To save an e-mail Office attachment to DocsToGo, tap and hold the attachment icon for about 5 seconds and you will get a menu of what you want to do with the file.  Select "Save it to DocsToGo".  This will open DocsToGo and display the document.

To edit a file tap on the screen somewhere in the middle of the document and a drop down menu will appear briefly at the top.  Tap the pencil icon at the top left to edit the file.

To save your file to your Google Cloud account, you need to have made some changes get the Save As option.  Adding an extra space between words counts but not adding a space at the end of a line.

To save a file tap the "<" icon in the upper left.  Then select "Save As" to bring up the "Save As" window.  You can then change the file name if you want (it defaults to the same name but with a number after it) or put in a new name.  You will also want to change the location to your Google Cloud account.  To do this tap the ">" at the right of the line with the default location.  This brings up the root directory of the save location.  At this point you can chose a subdirectory of you wish but you can only create subdirectories (folders) from your PC.

To print a file, tap the envelope icon in the upper left of the screen, after you have tapped the middle of the screen somewhere, and e-mail the file to the address you set up when you set up your ePrint account, typically something like xxx@hpeprint.com.

More general setup information.

What makes more sense is pay the extra money and sink with the cloud.  You can tell the program to sink every time you save a file.  It can sink with Dropbox (2 GB free), iCloud (Apple, 5 Gigs free), OneDrive (formerly SkyDrive and from Microsoft, 7 GB free), Google Drive (15 GB free including any Gmail you have), Box ($15/Mo for 1,000 GB) and SuperSync (which seems more geared to iTunes and not free).  To give you a feeling of how much space you might need, 1 Gig is enough for about 200,000 20 page word files (with no pictures) or about 1,000 pictures. One DVD stores about 4.7 GB.

 To save the DocsToGo file to the cloud, you must first have and account on one of the cloud services listed above.  I would recommend Dropbox or Google Drive.

To set up an ePrint or xPrint account with your printer, research what your printer supports.  The more high end HP printers support ePrint and I think some other companies do to. Apparently a lot of printers also support xPrint. You can purchase a device to turn most printers in to an xPrintserver device.  Amazon has them starting at about $90.