  Contributors to open source software packages often describe feeling
discouraged by the lack of positive feedback from users. This paper describes a
technology probe, Hug Reports, that provides users a communication affordance
within their code editors, through which users can convey appreciation to
contributors of packages they use. In our field study, 18 users interacted with
the probe for 3 weeks, resulting in messages of appreciation to 550
contributors, 26 of whom participated in subsequent research. Our findings show
how locating a communication affordance within the code editor, and allowing
users to express appreciation in terms of the abstractions they are exposed to
(packages, modules, functions), can support exchanges of appreciation that are
meaningful to users and contributors. Findings also revealed the moments in
which users expressed appreciation, the two meanings that appreciation took on
-- as a measure of utility and as an act of expressive communication -- and how
contributors' reactions to appreciation were influenced by their perceived
level of contribution. Based on these findings, we discuss opportunities and
challenges for designing appreciation systems for open source in particular,
and peer production communities more generally.
