Really Good Emails - A large collection of good product email design.
LibHunt - LibHunt tracks mentions of software libraries on relevant social networks. Based on that data, you can find the most popular projects and their alternatives.
Good Sales Emails - Best sales emails from great companies
GitNews Web - Trending repositories from GitHub, HackerNews & Reddit
Great Email Copy - A dose of emails from around the web.
Ruby Toolbox - Explore and compare open source Ruby libraries