[NobleExpress]

Real time GCs exist such as the IBM Metronome GC. Though I'll be honest and say I haven't heard of many real-time GCs other than the Metronome one. Certainly many new GCs have reduced pause times dramatically but that's orthogonal to real-time GC (as you can make pause times infinitesimally small but not let the mutator actually progress).

[mananaysiempre]

Here’s a fairly extensive review that mentions some recent research on “real-time” GCs, including one with a lower bound for mutator utilization: https://eschew.wordpress.com/2016/09/02/summarizing-gc/.

[pjmlp]

See PTC and Aicas.