capella has a direct connection to the sheet music library Musicalion.com. Here you can search and find your sheet music to download from around 60,000 scores - and you don't even have to leave capella to do so.
The search for "mozart divertimento" returns 25 hits immediately - with preview:
capella users who are not yet a Musicalion member can use a free trial. Persistent use of Musicalion.com is not free.
Now it's easy to share music on Musicalion because you can upload your score directly from capella. Musicalion works on a reciprocal basis: If you supply sheet music, you pay less for your membership.
...extend capella with special functions.
They are well sorted, easy to reach and helpfully described here:
And best of all: If you know programming, write your own Python scripts for capella.
Export sheet music directly from capella as a PDF. Doesn't play back, but looks good!
This is also possible: no sheet music, but a rich sound. This means that don't need the computer to listen to your works.
As a choir or ensemble director, you can create practice tracks for your choir or ensemble (if capella reader is not an option).
capella opens sheet music files from other programs: MusicXML, MIDI, capXML and cap. This is how the exchange with users of other programs succeeds.