SmallDevTools - Handy developer tools with a delightful interface
Iceberger - Draw an iceberg and see how it will float
LaunchKit - Open Source - A popular suite of developer tools, now 100% open source.
Stickman Builder - Free parametric graphic Stickman Builder, creates fascinating stick figures on the fly.
Profitable developer tools database - A database of 103+ hand-curated profitable developer tools
Drawy - Learn to draw, use camera to score your drawings