This is what I do with some of my spare time - within the last 12 months
- Realtime and historic Geospatial data. I've been using OsmAnd to log live route data to a web service and Bings's maps API to plot that data with JQPlot. In late 2019 I've finally integrated all this knowledge into a Follow Me system with it's own dedicated APK.
- Multi-factor Authentication - particularly client-side SSL certificates and TOTP as posession factors
- Mobile device security - in the light of the huawei (snooping) kerfuffle this is particularly interesting. AKA LinageOS on my S5
- CAN Bus Hacking and OBD-II adventures, mostly on my Volvo C30 1.6d DRIVEe
- Open source telephony, particularly around mobile applications
(but still periodically re-visited, or some how connected)
- A study of how not to DDOS your own distributed web application
- Using the Raspberry Pi as an Ocilloscope.
- Getting myself back up and running after installing CyanogenMod on my S3
- Nagios, as a system monitoring / exception reporting tool - notably to check more realistically than the default "is it alive".