Disclaimer: This is not another list of top/popular apps like Google Play.
Basically I'm aiming to collect here are all the apps that are useful, preferably without ads or annoying pay-only restrictions.
When I first got an Android phone, I knew at the time that there were apps to cover the majority of PC utilities and replace gadgets such as Satnavs, MP3 players, handheld media players, but it's only recently that I came across apps I would never have thought about, such as for roughly measuring sound and light intensity or even a smart alarm clock that wakes one up between a deep sleep cycle, instead of the shock of a noisy alarm.
Some apps I mention here are fairly obvious, but I thought I'd mention them anyway. If you've an old android phone lying about, it's worth seeing if any of the following apps can give it a new live, specifically the Tune-In Internet Radio apps. I left out the very obvious apps such as phone bundled apps, YouTube, Gmail, etc.
- marked apps have a banner ad in the app. If anyone knows of an ad-free version with the same or better functionality, please mention below.
Antennas - Displays nearby masts it detects on a map. (Limited to 2G with most phones.)
BitTorrent Sync - Like Dropbox, but doesn't use cloud storage, so a PC with shared folders must be online to work. Can be set to sync over 3G. Useful for automatic upload/download of photos, documents, music, etc.
CSipSimple - Lightweight SIP phone, can also be set to work over data. Integrates with the dialler so the phone gives a choice of cellular or SIP when you make a call.
Easy Toys - FlightLight, Ruler (inches & cm), Compass, Plumb line, Magnifier, Bubble level & Distance meter (rough). No ads either, at least at time of writing this.
Elixir* - Phone/task information app, including managing running tasks, CPU/RAM usage, sensor information, etc. Also unlocks certain low level features such as setting the phone to use LTE networks only.
ES File Explorer - Powerful file explorer, including root folder access and network & cloud drive file management.
FilmOn* - Portable TV, turns in most freeview channels (even outside UK) and various European satellite channels.
GPS Test - Detailed GPS satellite information, including satellite signal meters, accuracy, current speed, GPS coordinates and altitude. Can show the speed full screen, useful for checking the car speedometer's accuracy.
Light Meter* - Shows light intensity in lux along with an analogue gauge light. Quite a rough measurement, at least on my phone.
Navigator - Good offline Satnav. When installed, you tick which countries/regions you'd like maps for and it downloads these and then fully works offline, including voice, navigation and rerouting. Very useful for going abroad to avoid data roaming charges. Can also display info such as GPS coordinates, Altitude, speed, etc. on the map like a dedicated Satnav.
Nova Battery Tester - Benchmark the actual mAh capacity of the phone's battery. Useful for determining if the battery needs replacing.
OpenSignal - Displays all the phone masts around you, including based on 2G/3G/4G coverage type and optionally of neighbouring networks. Includes various tests such as data speed test and compass for nearest cellular mast or Wi-Fi.
Quickoffice - View, edit or create Word/Excel/Powerpoint documents.
Quick Settings - Toggle switches for settings such as Bluetooth, Wi-Fi, GPS, Brightness and Flash Light.
RealCalc - Scientific calculator, looks and works like a dedicated one.
RecentlyAdded - Displays contacts in recently added order. Very useful for finding a recently added number you can't think of the name of.
RemindMe - Reminder alarm clock. I recommend using a noisy MP3 file as its alarm sound, which is better than the SMS sound that may go unnoticed.
RTA Analyzer - Spectrum audio analyser (uses the phone's microphone.)
Simple mp3 Downloader* - Downloads pretty much any song keyed in. I won't say much more.
SleepBot - Smart alarm clock which tracks motion and optionally sleep talk through the night. Alarm goes off between 30 minutes up to the set alarm time when it determines the person is out of deep sleep to gently wake up. Pretty effective based on my testing.
Sound Meter* - Uses microphone to display sound level in dB along with an analogue needle meter. Seems pretty accurate - within 1dB of dedicated sound meter with noise above 40dB at least with my phone.
SoundHound - Like Shazam to identify playing music, but also works with sung and hummed music.
Speed Test* - App equivalent of Speedtest.net, useful for checking 3G/4G or Wi-Fi performance.
Tape-a-Talk* - Sound recorder. Can be set to record up to 44kHz, 16-bit wave files, although quality obviously depends on the phone's microphone.
Thermometer* - Displays in/out temperature like an analogue thermometer. Uses yr.no service using GPS for outdoor reading and battery sensor for indoor reading (only useful when out of standby.)
Translate - Takes a snapshot of foreign language text and translates it using Google translate. Needs Internet access, so only useful in a Wi-Fi area or if urgent using roaming data when abroad.
TuneIn Radio* - Internet radio. Can also be useful for turning an unusued old Android phone/tablet into an Internet radio, considering the price of dedicated Internet radios. Just connect to a Hi-Fi line-in socket or to a set of unused PC speakers.
TV Guide* - Detailed TV listings for most UK/Irish channels (not sure about elsewhere) and customisable list of channels showing now & next.
Ultrachron Lite - Stopwatch with multi-lap capability and history. Uses volume control to start/stop timing and for new lap.
Wikipedia - Download articles from Wikipedia for offline reading.
yr.no - Detailed ~10 day weather forecast, including 48hr hourly graph of rainfall, cloud cover, temperature, wind speed, direction, etc. Can show for specific towns or GPS location. No ads or premium-locked features either.
If anyone knows of any other useful apps that are not games, specifically apps on Google Play (unless very sure is malware free) that replace actual gadgets, please mention below.
Over time, I'll update this list with Apps mentioned below and any other useful ones I come across.