Local weather, does what it says on the tin.
We stayed in hotels/guesthouses a lot more than we expected (or really wanted) to. The filters on booking.com were great for finding somewhere with parking. Most of the time we didn’t actually book the place through the app, but turned up and checked it out in person first. Some places would quote us cheaper than booking.com when we arrived. Others would match the booking.com quote. For the very few places that refused to match booking.com, we just used their WiFi to book it through the app whilst standing in reception.
Our favourite app for navigation (also see Navmii). We downloaded offline maps to use it in countries where we didn’t have a sim card. However in a lot of Asia the offline maps didn’t work very well whilst driving and would often freeze.
Excel but free, stored online and available offline. We used this to document all the money we spent.
Easily the best app for overlanding. Map with wild camping spots, hotels, guest houses, mechanics, restaurants, launderettes, information about border crossings, and more. All except the photos are available offline. We used this every day.
When Google Maps failed us we used Navmii. You can download whole countries offline without taking up too much space on your phone. The biggest downside was that it would often take us on unnecessarily long detours. Lots of overlanders use maps.me but we only used this a couple of times and never really liked it.
Currency converter app. You can choose multiple currencies, and it will work offline. The rate updates when you go online. Especially handy when we moved between countries quite quickly.