Piggydb is described as 'Web notebook application that provides you with a platform to build your knowledge personally or collaboratively' and is a popular app in the Office & Productivity category. There are more than 100 alternatives to Piggydb for a variety of platforms, including Windows, Mac, Android, iPhone and Linux. The best alternative is Joplin. It's not free, so if you're looking for a free alternative, you could try Standard Notes or Microsoft OneNote. Other great apps like Piggydb are Evernote (Freemium), Simplenote (Free, Open Source), CherryTree (Free, Open Source) and NoteLedge (Freemium).
Joplin is a free, open source note taking and to-do application, which can handle a large number of notes organised into notebooks. The notes are searchable, can be copied, tagged and modified either from the applications directly or from your own text editor.