Customer IO vs Fastmail

Customer IO and Fastmail (Open-source software developed at Fastmail.) both appear on the Smoower Developer Ecosystem Index.

Customer IO (rank #165) holds a modest lead over Fastmail (rank #430) on the overall Smoower ecosystem score (51 vs 40). The gap of 11 points reflects composite signals across code, docs, community and reach.

On code quality (the state of repositories, tests, releases and polish), Customer IO is ahead of Fastmail. On education (docs, guides and learning material for developers), Customer IO is ahead of Fastmail. On community (issue response, PR reviews and discussion health), Customer IO is slightly ahead of Fastmail. On reach (how visible the ecosystem is beyond its own repos), Fastmail is clearly ahead of Customer IO. On momentum (release cadence and how fast the ecosystem moves), Customer IO is slightly ahead of Fastmail.

Customer IO carries 684 GitHub stars across 107 public repos, with 42 repositories active in the last 90 days and 26 external contributors on record. Fastmail shows 6,316 stars across 38 public repos, 12 active in the last 90 days and 2 external contributors. The star gap on its own does not decide the comparison, but Fastmail's footprint is roughly 9.2x larger, which usually shows up in downstream signals like inbound issues and third party integrations.

Customer IO is the stronger read for anyone weighting code quality. Fastmail looks better where reach is the deciding factor. The table below breaks the scores down pillar by pillar; the linked profiles cover the underlying repos, docs and community signals in full.