PurpleTrail - Whether it is about birthday or wedding party or holidays, you just need to name the event and PurpleTrail will provide you the apt invitation solutions.
Inkscape - Inkscape is a free, open source professional vector graphics editor for Windows, Mac OS X and Linux.
Evite - Send online invitations for all occasions by email or text message. Create invites for birthdays, baby showers, save the dates, or customize your own design.
Sketch - Professional digital design for Mac.
Zoji - As claimed by the developers of this Zoji, it caters online tools to aid you plan activities off-line.
Affinity Designer - Professional creative software, exclusively for Mac.