I love this program and find it indispensable. I have tried pretty much all of the free outliners out there over the years, but I always come back to TreePad for one reason or another. I may be in the minority here, but I like the fact that it does NOT save notes in RTF format, so the file sizes are smaller. It is also very fast and resource friendly as compared to other more bloated outline programs. Probably one of my favorite features is that when you perform a search, TreePad will list all of the nodes containing matching text; you don't see this feature on most other outliners out there.

As far as I can see, Treepad is available for Windows only and promises to work on Linux via WINE. That's fine, but it's not the same as being Linux native. Just so that's clear for any interested Linuxers.

[a couple additional thoughts:...]

1. TreePad is a tiny app with very little impact on your computer's CPU/RAM compared to Microsoft OneNote which, like most Microsoft apps, is kind of bloated and can be a system resource hog.

2. When you consider that TreePad is free (the Lite version is at least) and OneNote is somewhat expensive piece of retail software, that more the makes up for the clunky interface I mentioned in my previous comment.

Ultimately, quite an underrated app. Give it a try.

The interface may be clunky and outdated, but the app is actually loaded with an overwhelming amount of useful features and capabilities while still being easy to get up and running right out-of-the-box. The way it lets me organize my notes, records, etc. in a tree structure really lets you see the "big picture" of everything going on in my life and has greatly increased my level of productivity. I couldn't do without it now.

However, I did briefly try Treepad's popular competitor, Microsoft OneNote, and while it does have some key features that are lacking in TreePad, I found that keeping track of my data (i.e. being able to see that "big picture") was problematic and certain items inevitably got lost in the shuffle. I quickly went back to exclusively using TreePad and have used it ever since as my daily organizer.