Historically, one of the major problems on drupal.org is comparing multiple modules that all do similar things. See results of a survey of drupal.org users.
This group was created with multiple purposes around finding duplicate modules, analyzing their similarities/differences, and seeing if there is room for collaboration between them. Some times there are good reasons to fork a module, or similar looking projects can be very different when you actually use them, sometimes modules get released simply because people couldn't find what they wanted, or because they didn't realize they could file a patch instead.
Please use Wiki pages to post comparisons of projects which seem to be duplicates so they can be updated and expanded by other group members.
This group won't be dealing with module metrics and rankings - because that group already exists: http://groups.drupal.org/module-metrics-and-ranking it's about dealing with the 4000+ projects we have already, and hopefully leading to new and fruitful relationships between contrib developers.
See also a similar comparison of similar modules in the handbooks on Drupal.org.
Web Services vs Services
Web Services and the Services modules are the same aside from one difference: A custom implementation of OAuth....
Read moreSubscriptions vs. Notifications vs. Project issue's mail.inc
Here are some notes that I took while comparing these system, based on a couple hours of poking around and reading code. Anyone feel free to jump in here and correct me on any of this stuff, especially if you've actually /used/ either of these modules before. :P
Read moreContent recommendation modules
I think it'd be useful to have an overview of the various content recommendation modules in this group, and eventually a comparison review in the Handbook.
Warning: several of the modules listed below are under-maintained or abandoned. I've marked the more actively maintained ones (as of 01/2013). If it's not marked maintained, it's probably not.
Featured Content (Maintained)
http://drupal.org/project/featured_content
Read moreAggregation / Feed parsing Modules Comparison
A summary of feed-related modules and code.
Page needs updating
Feeds
Source: http://drupal.org/project/feeds
Description: Import or aggregate data as nodes, users, taxonomy terms or simple database records.
Status: Actively maintained
Aggregator
Description: core module that parses / aggregates feeds as non-nodes.
Current status:
- needs more flexible feed handling -- any invalid XML causes it to barf
- category system needs replacing with core taxonomy format
- more hooks to handle different types of feeds needed
