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logic-analyzer
Logic Analyzer, for Arduino, AVR, ESP8266 and STM32 with a very nice working processing interface, you could run it also on any Android device.
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InfluxDB
Power Real-Time Data Analytics at Scale. Get real-time insights from all types of time series data with InfluxDB. Ingest, query, and analyze billions of data points in real-time with unbounded cardinality.
If you want to really macguyver it, check out this little project to jury rig a rudimentary logic analyzer using your ESP8266: https://github.com/aster94/logic-analyzer (absolutely no substitute for a proper one, just to be clear).
NOTE:
The number of mentions on this list indicates mentions on common posts plus user suggested alternatives.
Hence, a higher number means a more popular project.