According to Georgian: A Reading Grammar by Howard I. Aronson, Georgian has many "harmonic clusters" consisting of two consonants pronounced with only a single release. (The consonants must be stops or affricates, I guess, but the distinction between stops, affricates, and fricatives in Georgian is something I don't understand very well since it seems that some phonemes can be rendered in multiple ways.)
The examples he gives, which are supposed to be exhaustive, are as follows (using the official romanization: apostrophe to denote ejectives, q to denote a uvular or thereabouts stop or affricate or fricative, and kh/gh to denote an unvoiced/voiced probably post-velar affricate or fricative):
bg, dg, dzg, jg pk, tk, tsk, chk p'k', t'k', ts'k', ch'k' bgh, dgh, dzgh, jgh pkh, tkh, tskh, chkh p'q', t'q', ts'q', ch'q'
My question is how these clusters are actually produced (and more generally whether Aronson's description is correct). It seems impossible to literally have a single release. What I suspect is meant is that the tongue starts with two points of contact against the roof of the mouth, but at the forward point it is held against the mouth rather loosely so that when the back stop releases the released air almost immediately causes the front stop to release.
It happens so fast that the releases are perceived as simultaneous and the writing system even puts the front stop first. I think I can produce such an effect when only stops are involved, but I find it hard to apply this theory to the clusters in the fourth and fifth lines above (those involving kh and gh).