Multiplans is a great tool. You can import and georeference geologic maps. I am using it when helicopter-assited sampling of larger areas. You can see your location and mark the sampling locations.
Oziexplorer and TwoNav are robust apps for offline navigation using calibrated maps. They both work quite well with a wide variety of formats. As to the geology apps, well, if you are looking for a mapping software, I think the best choice would be a GIS software for android, such as Quantum GIS. For some reason AcrGIS is reluctant to provide more support for Android/IOS platforms. Keep an eye on FieldMove software from midland Valley. They are doing a good job but apparently have not decided to go for the Android/IOS market.
For the modelling of geological structures, I suggest the use of Clino-MOVE app, which is one of the applications that Midland Valley Inc. produces for structural geology.
For Android I tried many different apps and founf found Locus maps very very useful (the free version is OK). It allows to make everything you need: record the track and add waypoints (both can be exported as kmz or other formats), open many different kind of maps/satellite image etc (both online and offline - just download the addon Map Tweak), open saved maps or kmz (e.g. waypoints, tracks) in different layers, ect. It is really a good app for field work. I have used it extensively while working in Ethiopia with a Google tablet, and I have to say that it is best I have ever tried.
For the Iphone/Ipod i can suggest you "GPS Kit" that is easy in tha App Store, and has very similar functions to Garmin handheld GPS , it can save tracks, way-points, routs and also it has dashboard to show altitude graph, speed situation, pedometer and etc.
This is the best app that i could find and i am using it everyday.
On Android devices, with Orux Maps coupled with Mobile Atlas Creator on PC, you have access to all map sources over the world. You can also create your own maps from picture files (screen copy for example).
For collecting structural data, Stereonet mobile and Faultkin mobile apps for iphone/ipad are the best for me as they offer a practical usage and data evaluation in the field.
I use SW Maps which was recommended by Prof Anas Emran from the UN-CRASTE Remote Sensing training centre in Rabat. Good for positioning photographs during a structural section
I'm testing Fieldmove, I have to say that apart from a few little bugs I find this an excellent app! great for exporting data to google earth, yet to be improved for Qgis
There are several thousands of mobile GPS Applications for Android and iPads mobile phones. However, their level of accuracy, functionality and efficiency differ.
This is why I could recommend the Polaris GPS Navigation and MapQuest.
I recommend these because they are well tested on the field and for practical class activities.
I strongly recommend OruxMap. You can add any maps with any coordinate systems. GPS accuracy goes up to 3 m, which is excellent for android phone. Download link is here: https://www.oruxmaps.com/cs/en/more/downloads
In the inland northwest US, many agencies and industrial forest landowners use georeferenced PDF map solutions like Avenza or other, similar apps for interactive, operational forestry work on mobile devices: https://www.avenzamaps.com/. The common solution is for the landowner to generate PDF maps of harvest unit boundaries or other treatment areas and provide these to the equipment operators or other contractors (tree planting crews, precommercial thinning crews, etc.) for offline work on their phones and tablets. I would say it has become expected in our area that mobile-friendly maps will be provided for most kinds of applied forestry work. Many foresters regularly use PDF-based solutions to record quick field data when doing iterative layout of timber sale units, silvicultural treatments, or prescribed burning operations. For example, establishing the locations of unit or harvest system boundaries, streams, fire line, and other feature layers. I know there are many similar solutions with the same functionality that include both free and purchase options. Hope that helps.