unifonter

unifonter is meant to be used as a filter, or as a quick lookup / translation tool. So you can use it either like

 $ man man | unifonter
 𝔐𝔄𝔑(1)                   𝔐𝔞𝔫𝔲𝔞𝔩 𝔭𝔞𝔤𝔢𝔯 𝔲𝔱𝔦𝔩𝔰                   𝔐𝔄𝔑(1)

 𝔑𝔄𝔐𝔈
        𝔪𝔞𝔫 - 𝔞𝔫 𝔦𝔫𝔱𝔢𝔯𝔣𝔞𝔠𝔢 𝔱𝔬 𝔱𝔥𝔢 𝔰𝔶𝔰𝔱𝔢𝔪 𝔯𝔢𝔣𝔢𝔯𝔢𝔫𝔠𝔢 𝔪𝔞𝔫𝔲𝔞𝔩𝔰

 𝔖𝔜𝔑𝔒𝔓𝔖ℑ𝔖
        𝔪𝔞𝔫 [𝔪𝔞𝔫 𝔬𝔭𝔱𝔦𝔬𝔫𝔰] [[𝔰𝔢𝔠𝔱𝔦𝔬𝔫] 𝔭𝔞𝔤𝔢 ...] ...
        𝔪𝔞𝔫 -𝔨 [𝔞𝔭𝔯𝔬𝔭𝔬𝔰 𝔬𝔭𝔱𝔦𝔬𝔫𝔰] 𝔯𝔢𝔤𝔢𝔵𝔭 ...
        𝔪𝔞𝔫 -𝔎 [𝔪𝔞𝔫 𝔬𝔭𝔱𝔦𝔬𝔫𝔰] [𝔰𝔢𝔠𝔱𝔦𝔬𝔫] 𝔱𝔢𝔯𝔪 ...
        𝔪𝔞𝔫 -𝔣 [𝔴𝔥𝔞𝔱𝔦𝔰 𝔬𝔭𝔱𝔦𝔬𝔫𝔰] 𝔭𝔞𝔤𝔢 ...

or

 $ unifonter Hello
 ℍ𝕖𝕝𝕝𝕠

Several different styles are supported; use -k followed by a style combination you want, otherwise one is chosen at random.

Supported styles can be seen via unifonter -d:

• 𝐁𝐨𝐥𝐝
• 𝐼𝑡𝑎𝑙𝑖𝑐
• 𝑩𝒐𝒍𝒅 𝑰𝒕𝒂𝒍𝒊𝒄
• 𝖲𝖺𝗇𝗌-𝖲𝖾𝗋𝗂𝖿
• 𝗦𝗮𝗻𝘀-𝗦𝗲𝗿𝗶𝗳 𝗕𝗼𝗹𝗱
• 𝘚𝘢𝘯𝘴-𝘚𝘦𝘳𝘪𝘧 𝘐𝘵𝘢𝘭𝘪𝘤
• 𝙎𝙖𝙣𝙨-𝙎𝙚𝙧𝙞𝙛 𝘽𝙤𝙡𝙙 𝙄𝙩𝙖𝙡𝙞𝙘
• 𝒮𝒸𝓇𝒾𝓅𝓉
• 𝓑𝓸𝓵𝓭 𝓢𝓬𝓻𝓲𝓹𝓽
• 𝔻𝕠𝕦𝕓𝕝𝕖-𝕊𝕥𝕣𝕦𝕔𝕜
• 𝔉𝔯𝔞𝔨𝔱𝔲𝔯
• 𝕭𝖔𝖑𝖉 𝕱𝖗𝖆𝖐𝖙𝖚𝖗
• Sᴍᴀʟʟ-Cᴀᴘꜱ
• 𝙼𝚘𝚗𝚘𝚜𝚙𝚊𝚌𝚎
• Ｆｕｌｌｗｉｄｔｈ

but note the order of the letters doesn't matter (-k bis is the same as -k sib), so if you find that you think "fraktur bold" instead of "bold fraktur", just go with it.

Some other options are supported; see the output of -h.