Simple tree notepad like editor [closed]

Try workflowy.com

The free plan is large enough for most needs.

It very nicely combines simplicity with depth of functionality.

I don't know how you feel about wiki-like editing, but it sounds like you could use wikidPad.

Maybe you could try Evernote. It has notebooks and tags which can be tree organized (at least they could be in version 2), so maybe that's OK for you? It's not open source though and you actually have to pay for the more advanced features (like OCR-ing and indexing your pictures).

Another possibility is TreeSheets. It's not tree oriented in the same way as the program you posted, it's table based - each table cell can have a subtable, with which you then make a tree structure. It's one of those things you have to try to see if it suits you, but I find the concept very interesting. Also not open source, but it is freeware.