Update January, 2020 - WebCards https://sourceforge.net/projects/webcards/ is abandoned. I'm not sure at what point it becomes abandonware. But, the site is not only 404 now but not even left parked for the software to have a come back. Kind of annoying for me. I paid for the full version which isn't working now. But, what can you do? Find a replacement. Isn't that what brought you here to Alternativeto.net ?
As the only good choice so far there isn't a lot to add for a review. I wish this was more actively developed but, I don't think there is a strong demand for online greeting cards any more.
WebCards does work. There is a free option, older software which does still work. Or, you can make a one time payment and have the premium version with a few extra features. If you want to sell your greeting cards, the premium version is necessary. If you just want to offer your art on web cards/ ecards for free, then you don't need the premium software.
I wish the software worked a little smoother but overall it is good. Even if it is the only option worth reviewing, it is still a good way to showcase your art and get people sending it to each other, hopefully.