Yesterday, I saw this link published on twitter via @element14
And this made me think about how I use my i-devices in my engineering life and decided to tell the world. The first thing to notice is that a lot of my work happens on the computer, much like most of you out there - I assume. I then go down to the labs to build, test etc and often my notes / books / scribbles were left upstairs or I did not bring all the notes I made or I left my calculator HP48G either downstairs or upstairs but never in the location where I needed it. I thus thought about the question of which engineering app and concluded some of the apps I need for engineering are actually not "real" engineering app but my engineering requires them for a smooth flow of work. I use an iPhone and iPad for my little office travels.
My setup:
Dropbox account (free)- drop box allows you to share files across multiple devices including iPhone and iPad. And thus all the documents, datasheets and scribbles (btw I also, have an Livescribe pulse pen which allows me to write down scribles and notes and make circuit drawings which I can store on my computer instead on paper alone and thus digital) are under my finger tips through the dropbox apps. Any datasheet that I do not have I can find on the web and store in my drop box.
I use: A PDF editing app called iAnnotate which allows me to make notes directly in the datasheets and import and export to and from dropbox. So, I have all my notes directly in the datasheet I need for my project.
Electronic Toolbox pro (well worth the price)- this app allows you basically to do everything to that various free applications do such as: codes and specifications for most of the components you'll ever need and it allows for a project management setup through which you can plan your projects and keep together various data sheets for different components and pinouts for pics and connectors. It also features various calculators and converters.
M48G calaculator (free)- I used this calculator at university and to have it in my pocket all the time is heaven. The great feature of this version is that with a simple swipe you can switch between a simple version with big buttons but still scienctific use and the complex version with all the functionality - although the buttons are slightly smaller.
Graphing on the M48 is not great and editing functions is not easy either so for this function I use the free Scientific Graphing Calc.
Is there anything I need to find or refresh my memory about mathematical equations I turn to the Wolfram Alpha app.
The above apps I use on a regular basis especially when it comes too testing, building and adjusting of designs when I am not near my computer and dropbox keeps all portable and transferable.
There are other apps I use albeit sometimes more as a gimmick which are:
Matlab, iCircuit, etools lite, math ref free, formulate pro, AWG convert, NI Pinouts, etools lite,pocketsCAs, MissingCalc, RPN calc, pi cubed lite, iTunesU, Mathstudio, formulus free, iFormula, uits converter, e-laboratory, dipswitch, freqGen, Electrical Toolkit, sensorWiki.
But too be fair, since the Electronic Toolbox Pro came out a lot of them became obsolete which clears some space on my devices.
If you think after reding this that there is definitely an app I missed then please let me know. Work flow can always be further smoothed out.
My2p
ps. By the way, the setup I have requires some kind of wifi / internet because otherwise things do not work properly (lol what does these days).
pps. For ease of use I provide various links to the various apps but I am not affiliated with any of them and as far as I am aware I do not get commission.
ppps. If you do not have a dropbox account yet, please sign up via this account http://db.tt/PWX6Voob and we both get some extra space and I could use some more for my studies - yes, you would be supporting a hard working student 
- ps. the extra space becomes available when you install dropbox on your computer.
pppps. Yes, I have the element14 app on my phone but I cannot wait for a decent upgrade because at the moment the app does not contribute anything at all to the website user experience.