The Best Free Software
Notepad++ is a free source code editor and Notepad replacement that supports several programming & script languages. Great plugins such as NppFTP and Compare make it really usefull for quick code fixes on the webserver.
FileZilla is open source FTP software for putting files on and off the server. FileZilla makes managing files on server so easy as you would be working localy in file explorer.
An Open Source vector graphics editor, with capabilities similar to Illustrator, CorelDraw, or Xara X, using the W3C standard Scalable Vector Graphics (SVG) file format. Inkscape supports many advanced SVG features and great care is taken in designing a streamlined interface. I used it to design this HTML Color Codes website.
GIMP is free PhotoShop alternative. It is a multi-platform tool suitable for a variety of image manipulation tasks, including photo retouching, image composition, and image construction. It can be used as a simple paint program, an expert quality photo retouching program, an online batch processing system, a mass production image renderer, an image format converter, etc.
IrfanView is a very fast, small, compact freeware software for viewing/converting/renaming/copying images and A LOT more. It's strong side is ability to batch convert many images at once with very little effort... It supports incredible amout of image types and you can expand it's functionality with plugins.
License: Freeware, but only for private, non-commercial use
RIOT - Radical Image Optimization Tool
RIOT is a free image optimizer that will let you to visually adjust compression parameters while keeping minimum filesize. It uses a side by side (dual view) or single view interface to compare the original with the optimized image in real time and instantly see the resulting file size. RIOT is a must for optimizing images for websites. It's also available as IrfanView and GIMP plugin.
Replace in Files
It does only one thing but it does it perfectly. If you need to replace text inside many files that are scattered inside many folders and subfolders you can do it in a few seconds with this tool. It can save you A LOT of time.
Agent Ransack is an award winning file searching tool, that can search for files by part of file name, file contents, size, date modified... If the file exists you will find it with this tool.
7-Zip is open source file archiver with a high compression ratio. I will unpack file types 7z, XZ, BZIP2, GZIP, TAR, ZIP, WIM, ARJ, CAB, CHM, CPIO, CramFS, DEB, DMG, FAT, HFS, ISO, LZH, LZMA, MBR, MSI, NSIS, NTFS, RAR, RPM, SquashFS, UDF, VHD, WIM, XAR and Z.
It also offers strong AES-256 encryption in 7z and ZIP formats.
The Best Online Services
PunyPNG is a PNG compression and image optimization tool developed by Gracepoint Berkeley. This is probably the best free online PNG optimization tool.
Another image optimizer but this one is from Yahoo. Smush.it uses optimization techniques specific to image format to remove unnecessary bytes from image files. It is a "lossless" tool, which means it optimizes the images without changing their look or visual quality.
Page Speed Online
Page Speed Online analyzes the content of a web page, then generates suggestions to make that page faster. Reducing page load times can reduce bounce rates and increase conversion rates.