Well, it was easier than I thought (well, not really, let’s say as easy as it should be):
gem list rhc --remote --all
Which returns:
*** REMOTE GEMS ***
rhc (0.84.15, 0.84.13, 0.83.9, 0.82.18, 0.81.14, 0.80.5, 0.79.5, 0.77.8, 0.75.9, 0.74.6, 0.74.5, 0.73.14, 0.72.29, 0.71.2, 0.69.6, 0.69.3, 0.68.5)
rhcp (0.2.18, 0.2.17, 0.2.16, 0.2.15, 0.2.14, 0.1.9, 0.1.8, 0.1.7, 0.1.6, 0.1.5, 0.1.4, 0.1.3, 0.1.2)
rhcp_shell (0.2.12, 0.2.11, 0.0.9, 0.0.7, 0.0.6, 0.0.5, 0.0.4, 0.0.3, 0.0.2, 0.0.1)