In the last few years my company Robert Deutz Business Solution was focused on creating usable and accessible Joomla! extensions but there wasn't an appropriate place to publish them. Uploading everything to github or something similar does not make much sense because to integrate it in a site so that the result is still accessible is not an easy job so supporting people over the integration is a really good idea.
Most of the extensions you will find are free of charge but some for very special business cases are only available with a paid membership. So you can download my addPHP plugin or my event calendar for free but the government organisation directory or the refuse collection service component is not a free download. All extensions are published under GPL.
We are still in the process of moving anything to this site, so keep an eye on it for new things.