A Screenshot of the Graph 89 App from the Google Play Store
As the name would allude, this app is an emulator for a TI-89 calculator. After downloading this app, a ROM image of the TI-89 needs to be obtained. A quick Google search or a visit to TI’s website and this ROM can be downloaded easily. All of the features of the TI-89 such as the CAS functionality and graphing are fully functional. The best part of this app is that it's free! A paid version is available though that allows the user to emulate other calculators such as the Ti-84 and TI Voyager. To download this app you can search the Google Play Store or follow these links: You can download the paid version of the app here, and download the free version of the app here.
Hex Converter Plus
A Screenshot of the Hex Converter Plus App from the Google Play Store
Some engineers deal with hex, binary, and decimal conversions a lot. Having quick access to a tool to convert between numbering systems can be very useful. In addition to engineers, this app can also be beneficial to a lot of electrical and computer engineering students, just don't expect to be allowed to use this on an exam! To download this app head over to the Google Play Store, or there's a short cut here.
A Screenshot of the ElectroDroid App from the Google Play Store
ElectroDroid is a collection of various electronic tools and references packed into a single app. It contains a lot of different tools such as a voltage drop calculator, a resistor color code decoder, LM317 voltage regulator calculator, and the list goes on. Take a look at the complete list on the developer's website. This app is available in a free ad-supported version or a paid version. To download this app you can search the Google Play Store or follow these links: You can download the paid version of the app, ElectroDroid Pro here, and you can download the free version of the app here.
A Screenshot of the Droid Tesla App from the Google Play Store
Droid Tesla is a SPICE circuit simulator for your android device! Unlike some of the other SPICE simulators that only support a small number of components, Droid Tesla has a large list ranging from Logic Gates to JFETS. This app is available in two versions. A free version is available that has a limited about of components. A paid version, presently listed at $12.00 USD, contains a wider range of components. To download this app you can search the Google Play Store or follow these links: You can download the paid version of the app, here, and the free version of this app, here.
Adafruit's Circuit Playground
A Screenshot of the Adafruit Circuit Playground App from the Google Play Store
Although geared more towards than enthusiasts than engineers, this paid app contains a handful of tools that can be powerful for many users! This app contains several smaller tools such as a datasheet search, wavelength to color converter, voltage divider calculator, hex/binary/decimal converter, and it also gives the user access to "exclusive deals" from Adafruit. For a complete list of features, and to download the app, go to the Google Play Store or use this shortcut here.