Did you test it @molly? Feedback is welcome.
I have now
At first sight things are looking good and polished (it is a form of art so, worth to mention).
The two things that annoyed me (sorry, there is no way for me to tell it more gently).
1) if i press right mouse button to view the json file, i seem unable to 'return' to the initial packager view. All things i tried (click close, escape etc) closes the window (which is not what i wanted).
2) i chose to automatically extract the package, which automatically seems to popup a windows explorer window at the location where the package was extracted. I absolutely most definitely despise those windows popping up as i do not use Windows explorer _ever_ (which is more my personal problem ofc.) :-)
For 1, it needs a solution in the end (unless i missed something obvious) for 2 i would be in your debt in case there is a possibility to prevent that from happening.
In case not already having considered, i would have expected the download location to be part of the options inside the online package manager. At least don't let me start selecting a directory from my computer top-level but in user dir or lazarus dir (i usually install my packages alongside lazarus install dir for lazarus 1.7 series).
After i managed to convince my firewall that lazarus indeed requires some internet access (all requesters before that worked splendid as far as i am able to tell) the list was populated with about 8 packages. The treeview is easy to view and works as expected.
Downloading and extracting seems to have worked like a breeze, at least i did not encounter any issues.
Question: I assume (?) that you also add support for installing the packages, in which case the question pops up: what if i already installed packages manually ? would the online package manager be able to detect that and not try to install the same package twice ?
There are many of such questions that comes to mind but, i promised to keep myself out of things until things become more stable for you. There is no point in speculating until things become more clear for you and you have set a more definitive goal for yourself. Especially because "i want it all, and i want it now" (think electrical guitars and high pitched voices ;-) )
I have to congratulate you on your progress, as things that work seem to work as expected for me. In that regards never mind my encountered annoyances. Most probably you are aware of them already anyways.
Thank you for your hard work on this and actually realizing something that should have been done/implemented ages ago.
edit:
Oh, i almost forgot. If no package selected, download button is active. Dunno how hard it would be for virtualTV to determine number of selected items, otherwise can be solved adding a counter at onclick event/on check event and only activate download button when items are actually selected ? Would imho be better than the nice message box you now show