Not really an app, but what scuppers all my Linux attempts is documentation. Case in point: I'm trying to set up a RAID server with heterogeneous drives of various sizes. I had to have someone tell me to look at mdadm and LVM, which I am now doing, but most articles seem to pertain to older kernel versions (2.6/2.8, ArchWiki doesn't even seem to have a date on articles) and I have no clue if such older info is still relevant, outdated, in-between... I'm stuck.
My last try before that, I had to resort to trial-and-error to create upstart jobs (is there a user doc, anywhere ?), and ended up using the wrong virtual terminal software (there was mux, and.. xterm, I think ? can't remember) because that's what Google came up with, and I had no clue where else to start.
And before that, I had to spend hours trying to get dual-screen to work acceptably, and in the end I couldn't (something about having 1xATI +1xnVidia card w/ different-definition screens, and wanting to watch videos, brought the whole house down)
So... not sexy... not peer-reputation/hacker-cred enhancing... but I'd strongly advise to work on documentation, not apps.