LaTeXiT is not available for Linux but there are some alternatives that runs on Linux with similar functionality. The best Linux alternative is KLatexFormula, which is both free and Open Source. If that doesn't suit you, our users have ranked more than 10 alternatives to LaTeXiT and six of them are available for Linux so hopefully you can find a suitable replacement. Other interesting Linux alternatives to LaTeXiT are TexMaths (Free, Open Source), EqualX (Free, Open Source), Apache OpenOffice Math (Free, Open Source) and Mathematical LaTeX Helper (Free, Open Source).
TexMaths is an addon designed to provide LaTeX support into LibreOffice. LaTeX equations can be inserted as images (SVG or PNG formats) and the LaTeX code is saved into the image attribute for further editing.
Math, part of the Apache OpenOffice suite, is a tool for creating and editing mathematical equations, similar to Microsoft Equation Editor (included in Microsoft Office). The created equations can then be embedded inside other OpenOffice.
This tool provides a very simplistic gui that renders LaTeX-expressions directly while typing and is able to copy the rendered images to the clipboard or alternatively save them to the desktop while maintaining transparency information.