I'm using this to take notes during and organize thoughts after scheduled Skype foreign language lessons. I naturally lean towards making outline lists when note-taking, which works wonderfully in TaskCard. I haven't yet taken advantage of the TaskCard-Calendar integration, but I'm happy that for a cross-platform user like myself, Gmail calendars can be manipulated by Calendar using TaskCard. (I'm an Android person with a Mac. Blasphemy!)
There are still times where this app crashes for me. Notably, I can't seem to nest existent cards inside other existent cards, although I seem to be able to do this with blank cards easily enough. I also experienced problems when trying to maximize a card, wherein I was stuck on a separate desktop from my maximized card, but was eventually able to go to Window > Zoom to get out of full screen mode.
I hope the dev is still actively developing -- it seems to have been six months since the blog last updated -- but regardless of future developments, I think $15 is a reasonable price for something that will prevent me from falling back on my terrible old workflow of having half a dozen TextEdit windows open at a time, trying to remember which ones to save on shutdown and which to delete.
Ability to export to RTF, MD, HTML, TXT, or anything more portable than proprietary format would bring this up to 5 stars, even with the occasional crash.