One of the only movies that remains intriguing throughout despite being basically a single conversation.
Some of my favories:
Coherence (scifi)
Garden Party (sleazy young adult Los Angeles drama)
Murder Party (low budget horror comedy)
How English sounds to non-English speakers (youtube)
Circle 2015 (scifi)There's some play adaptations which have few characters and mostly dialogue: Carnage, Who's Afraid of Virginia Woolf, Glengarry Glen Ross
Linklater's "Before" trilogy is also heavily dialogue-based, but the there are multiple locations.
"Perfect Strangers" (2017) [1].
And so is, mostly, "Rope."