Quickmath
Quickmath is a LaTeX package I wrote to solve a few problems related to typing mathematical documents, especially quickly (e.g., keeping up while typing notes in a class). Mainly, math uses lots of environments and special fonts. Repeatedly typing \begin{...} and \end{...} and \mathbb{...} is slow and makes the code look cluttered.
The quickmath package defines a large collection of theorem-like environments. More importantly, there are shortcuts so that the user doesn't have to type \begin{...} and \end{...}. For example, \thm begins a theorem environment, and \ethm ends it. (Other environments generally use common blackboard abbreviations: \prop...\eprop, \lem...\elem, \pf...\epf, etc.). This makes the typed code look very similar to what's written on the board:
\thm
There are infinitely many primes.
\ethm
\pf
...
\epf
These shortcuts significantly reduce the barrier to learning LaTeX. In addition to these environments, the quickmath package defines a collection of common symbols, such as the blackboard bold set symbols (\R, \Q, \Z, \N). Finally, the quickmath package provides two useful options: nosections, and hidedetails.
In documents with sections, the default numbering for theorem-like environments defined in the quickmath package is that all such environments are on the same counter and are displayed as <section number>.<counter>. E.g., Theorem 1.1, Definition 1.2, Proposition 2.1, and so on. In documents without sections (like homework or exams), the nosections option changes the numbering to ignore the section. So you'll instead get Exercise 1, Exercise 2, and so on.
The quickmath package provides a hide-able environment, which could have several uses. When the global option [hide] is invoked, anything throughout the document of the form \hide[<spacing>]...\ehide is suppressed. The optional argument specifies an amount of vertical spacing which is typeset in place of the content. For example, use \hide...\ehide to enclose the solutions to a problem set. Then, you can produce the problem set by compiling with the [hide] option, and produce the solution set by compiling without it.
To start using the quickmath package, download the .sty file, put it in the same folder as your .tex file, and add \usepackage{quickmath} to the preamble of your .tex file. For more information, download the documentation.