Font Manager might be a bit more popular than Holdkey. We know about 1 link to it since March 2021 and only 1 link to Holdkey. We are tracking product recommendations and mentions on various public social media platforms and blogs. They can help you identify which product is more popular and what people think of it.
I used Holdkey for a while because I needed so many special characters. Not sure it's a good solution for em-dashes though. Source: almost 3 years ago
The font-viewer that is part of font-manager can do it. Source: almost 2 years ago
WinCompose - WinCompose supports the standard Compose file format.
NexusFont - Choose and manage your fonts with Nexus Font.
PopChar - The character map that works!
AMP Font Viewer - Jump to Download - Download.
AllChars - If you're new to AllChars: start with the Introduction, see the FAQ and Manual. And finally download it. AllChars is now Open Source, usage is free and the sourcecode is available.
Font Viewer - Font Viewer is an application which does exactly that - it views fonts!