I have a "log file" for each week, broken down by day where I keep track of my TODOs and check them off. I put little notes next to the todos that describe what exactly I did, but not in much detail. But I can easily go back to 12/05/2011 and see exactly what I did that day. I usually plan one week in advance, but I only put task details there once I actually figure them out.
"What did I do last time I worked on that project or for that client?" is more difficult. I'm a fan of using blossom.io + Slack (slack.com) for large projects or startups. Usually there is only one such project I am working on. If you have lots of different project then these tools may cause too much overhead...
I'm using a desktop wiki : http://zim-wiki.org/
I use it in a messy way, but it's what i want : take a note quickly.
I create a page by day with the calendar and there is a full text search tool for when I need to find and old note I also like the task plugin : you put a todo mark in any page and you have an icon to regroup all the "todos". I put some keywords sometimes, to help to remember later or when i'm using the search tool.
There is a picture plugin, but it's just keeping a link to the real picture, so it's lost when you move it.
I know there is the same kind of tool for vim, but i didn't try it.
I've just started playing around with Harvest (getharvest.com); it might be worth checking out if you're already using some kind of task-manager (because they integrate with tools like Asana). Makes it easy to see what you did, which projects it was for, and to bill the client accordingly.
Wiki on a USB stick :D https://www.dokuwiki.org/install:dokuwiki_on_a_stick
Get synkron, configure it to mirror your wiki to a harddisk as backup and you're set.
At my job we have a JIRA server running. It is a big enterprise piece of software, but you can log stories and tasks pretty well. If it were up to me I would use something else, albeit I am not sure what that is.
When I was on my own, I used Google Doc to keep track of daily logs in a loose way. I am getting a team so I switch to asana. It has been for 3-days I am fine with that.
Workflowy works great but sometimes it gets tricky (depending on how you'd like to format things).
Workflowy (https://workflowy.com/) is my goto for keeping lists, planning, and tracking my work/project logs.
For work, I have a section structured as such: Work > {CLIENT} > {YEAR} > {MONTH} > {DAY, HOURS, SUMMARY}
e.g. A day's entry might look like:
8/13/2014, 6.75h, One-liner summary of the big ticket accomplishments today * 11 - 12,30, 1 - 6,15 * [x] #ASAP Task 1 description * [x] Task 2 description * [x] Task 3 description * [x] Meeting with @client @coworker1 * Notes from meeting... * More notes...
I track my hours worked in shorthand and format {DAY, HOURS, SUMMARY} because I dump and parse the data at the end of the month to generate my invoices.
SQL, Markdown, or code snippets is a little trickier, but you can hang multi-line text as a sub-node using SHIFT+ENTER. In general, Workflowy offers a ton of great keyboard shortcuts and pretty decent search capability. Media attachments would need to be as URLs AFAIK.
I've been using it for 2-3 years and if they ever decided to close shop, I would seriously try spinning up a similar service.