Hello,

I don't know how I missed this software for so long... I just found out about Calligra Plan...

Anyway... Is it possible to share resources between projects? In a way similar dotProject does, for instance... If not, is it possible to import resources from another project?

Not certain exactly what you mean. (don't know dotProject)
Two possibilities exists:
1) Import resources can be done running the script from the menu Tools->Scritps->Import->Resources from Plan file. This will import only resources (and calendars).
2) You can also use the Tools->Insert Project File. This will import the complete project (ex scheduled data)

If you want to use the same resource in multiple projects, imo the easiest is to maintain a separate file with just the resources which you import when you start a new project.

Also if you want to take multiple projects into account when scheduling to avoid doublebooking the same resource, you can export/import bookings.
This is implemented as 3 (python) scripts you can run from the Tools->Scritps->Resource Busy Information menu.
Note that this depends on that the resource ids are the same, so Plan knows it is the same resources. This is taken care of if you maintain a separate resource file.
It also depends on the project ids to be different. This you can ensure by:
* Always start from a template, or
* If you want to start from an existing (similar) project, use the Tools->Insert Project File. This will also import any resources along with tasks etc, but will keep their ids.