ポツリポツリ

雨あめがポツリポツリ(と)降ふるfor rain to fall in scattered drops
空そらを見み上あげると、雨あめがポツリポツリと降ふり出だした。
Looking up at the sky, I noticed rain beginning to fall in scattered drops.
ポツリポツリ(と)話はなすto speak haltingly, bit by bit
彼かれは緊きん張ちょうしながら、ポツリポツリと話はなし始はじめた。
Nervous, he began to speak haltingly, bit by bit.
〈人ひと〉がポツリポツリ(と)集あつまるfor people to gather in ones and twos
開かい場じょう前まえから、人ひとがポツリポツリと集あつまってきた。
Even before the doors opened, people had started gathering in ones and twos.

Related words

ポツポツN1
ポツリポツリ emphasizes distinct occurrences separated by clear pauses, while ぽつぽつ can describe a slightly more continuous or gradual progression.
ちらほらN1sense 1
ちらほら describes things appearing here and there in small numbers, similar to ポツリポツリ's sense of sparse occurrence, but it lacks ポツリポツリ's rhythmic sense of pause-then-repeat.

ザーザーN1sense 2
ポツリポツリ describes rain falling as a few scattered drops, while ざあざあ describes rain pouring down heavily and continuously.

しとしとN1sense 2
ポツリポツリ describes rain falling in a few scattered, separate drops, whereas しとしと describes a steady, quiet drizzle falling continuously.

Onomatopoeic/mimetic word; the repetition of ぽつり (sound of a drop or a small isolated thing) suggests sparse, intermittent occurrence.