File extension:

.chm

Format:

One CHM file contains the entire help.

Platforms:

All Windows versions since Windows 98

Typical use:

Local online help for applications installed on the user's computer

Table of contents:

Yes. Integrated in the CHM file and always visible in the viewer. Excellent, immediately intuitive navigation for the user.

Keyword index:

Yes

Full text search:

Yes

Context sensitive help:

Yes, full context-sensitive help support. Can include text-only field-level popups which can be displayed directly within your application without the main help window.  

Popups:

Yes, both in the help viewer and for context-sensitive help. Natively, HTML Help only supports text-only popups without formatting or graphics. Only these plain-text popups can be used for field-level popups displayed in your application.

You can also use Help+Manual's JavaScript popups in HTML Help. In addition to formatted text and graphics JavaScript popups also support hyperlinks and even videos and animations.

You cannot mix JavaScript popups and plain-text popups in a single project but you can create a separate project containing only your plain-text popups if you want to include JavaScript popups in your main project.

Multimedia:

All Windows-compatible video formats are supported, along with online video services. However, support for playing the formats used must also be installed on the user's computer. For example, if you use a DiVX video don't expect it to be playable on all user machines!

Generally speaking, MP4 video is the most reliable video format. However, if you want guaranteed compatibility it is best to put your video on an online service like YouTube or Vimeo. Then they will automatically handle the compatibility issues by generating multiple versions of your video and serving up the correct one for the current user.

Printable by user:

The Print function of HTML Help is very limited. The help viewer can print topics and chapters but each topic is printed on a separate page.

Pros:

Single file containing all topics, graphics and the table of contents. Intuitive, directory tree style table of contents that is always visible to the user. Flexible formatting with HTML (in Help+Manual you have full control over your topic pages with HTML templates), including the ability to add functions with JavaScript etc. by adding your own code to topics and templates.The HTML base makes it easy to produce a browser-based version for the web that looks almost identical to the HTML Help version.

Cons:

Popup topics are limited to plain text in native mode. Severe restrictions on deployment in networks and the Internet, primarily suitable for help installed locally on the user's computer together with the application.