First of all, the compass. And there are very many to choose from! This is less than half of Play Store's offering.
I've chosen Smart Compass.
It does the job well, and without the clutter or unnecessary complexity that some have. Just be careful when using this - as with any compass - that you don't have any magnetic source nearby, which would result in a false reading. I have a magnetic catch on my phone case, which is a slight complication.
When we're out on the cut, I keep a log of where we moor at the end of each day. I do this in case we ever have cause to phone emergency services. Having readily to hand the details of where we are could be a life saver. And the best piece of information the emergency services can have is our grid reference, accurate to 10 metres. I use the Grid Reference app, again for its absolute simplicity.
It's not often we want to know how fast the boat's going. I expect walkers and cyclists don't often need to know their speed, either. But when we do want to know, like when we were on the River Trent last month, then we use this Speedometer app.
As the creators say of it, it does what it says on the tin. There are, as you might expect, loads of different apps which do much the same job, each in their own way.
While walkers might find the speedometer useful, much more so for them is the Pedometer. Boat crew doing the locking, with walks between locks as well as around them, will find the data this supplies interesting.
I hope this series has been interesting, useful. If you know of any other apps which might be useful to canal users, please tell us about them in a comment below.