Top 4 C++ Aviation Projects

GAAS

12 1,840 0.0 C++

GAAS is an open-source program designed for fully autonomous VTOL(a.k.a flying cars) and drones. GAAS stands for Generalized Autonomy Aviation System.
RTLSDR-Airband

21 705 7.3 C++

Multichannel AM/NFM demodulator

Project mention: Listen to HD radio with a $30 RTL SDR dongle | news.ycombinator.com | 2023-11-05

You're all correct, except there are not that many $30 SDRs out there. Also, most SDRs have clearly superior capabilities to the RTL-SDR, though those capabilities often are not required.
BTW, for simple AM/FM demodulation I cannot recommend enough the handy https://github.com/charlie-foxtrot/RTLSDR-Airband. For example most of LiveATC.net feeds run on it.

InfluxDB

www.influxdata.com sponsored

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.
XCSoar

4 322 9.8 C++

... the open-source glide computer
mscsim

4 286 2.8 C++

Simple flight simulator.

NOTE: The open source projects on this list are ordered by number of github stars. The number of mentions indicates repo mentiontions in the last 12 Months or since we started tracking (Dec 2020).