Python 3: Alfred-Workflow, by Adam Hitchcock
Python 3: Ualfred, by @chaojie
Dart: Alfred Workflow, by Klemen Tusar
Go: go-alfred by Jason Cheatham
PHP: Alfred Workflows PHP Helper by @joetannenbaum
Other Utilities
Add auto-updating to your Workflow: OneUpdater, by @vitor
iTerm2 intergration: Custom Alfred iTerm Scripts, by @vitor
All the libraries on this list are (at the time of the last edit) up-to-date and their developers are either still supporting them or forum regulars. That means any problems you find and suggestions you have are likely to be addressed.
If there’s any library you think belongs in (or should be removed from) this list, leave a reply below. I’ll evaluate it and then hide the comments (so the thread can be kept tidy).