#active development

Fira Code

Fira Code was inspired by Hasklig font: Ligatures for Haskell code

Fira Code, like Hasklig, adds ligatures for operators normally comprized of multiple characters. Fira Code is based on Fira Mono. If your editor supports this it's definitely worth checking out.

Hasklig

Composite glyphs are problematic in languages such as Haskell which utilize these complicated operators (=> ->= etc.) extensively. [...] Hasklig solves the problem the way typographers have always solved ill-fitting characters which co-occur often: ligatures.

Hakslig enhances Source Code Pro with ligatures for operators normally comprized of multiple characters. If your editor supports this it's definitely worth checking out.

Everson Mono

"Everson Mono is a simple, elegant, monowidth font. I started designing it in 1994 primarily to make glyphs available to support the non-Han characters in Unicode and ISO/IEC 10646, though I hope that users may find it a pleasant alternative to Courier and Monaco for general purposes, e-mail, and so forth. I have found it quite legible at sizes as small as 4 points. It is lighter and a bit looser than Courier."

Michael Everson's project has been running for over 20 years. As a result this is a well rounded font with impressive coverage. In recent years it has been updated with bold and italic versions. The interests of the creator of Everson Mono are reflected in the many languages in Evertype Publishing's portfolio. As a writer's font, it lacks a distinct zero.

Creep

This pixel font (really only works at one size, no antialiasing) is great for tiny text. It's a bit specialized at that, but perfect if it's what you're looking for.

DejaVu Mono

"The DejaVu fonts are a font family based on the Vera Fonts. Its purpose is to provide a wider range of characters while maintaining the original look and feel through the process of collaborative development (see authors), under a Free license." ...

The DejaVu project is open source at its best. Started by expanding the coverage of the Bitstream Vera typeface, it has been in active development for the past ten years. You might not have missed the Turkish Lira sign, but if you did you'll be glad to know it has recently been added. DejaVu has an amazing coverage and has all the styles you'll ever need. It's classic and understated and the goto font for many coders.

Fantasque Sans Mono

"A programming font, designed with functionality in mind, and with some wibbly-wobbly handwriting-like fuzziness that makes it unassumingly cool." ...

Conceived as the "the mutant child of Comic Sans and Helvetica Neue", this is fun as a programming font can get (legally at least). Make no mistakes though, this isn't Comic Sans and Fantasque Sans Mono is very serious. The open source project has seen a great many updates throughout the year. Add a dash of wibbly-wobbly to make a day of debugging a bit less dreary.

GNU Unifont

"This version provides full coverage of the Unicode 7.0 Basic Mulitlingual Plane (BMP). The BMP is the first Unicode "plane" of 65,536 code points, and has character encoding for most of the world's modern scripts. As of 20 June 2008 (by coincidence the Summer Solstice), GNU Unifont had a glyph for every printable code point in the Unicode BMP." ...

Another typical GNU project, it's like a sans version of the GNU Freefont. Not in style but in intent: its coverage is equally amazing and the project is also very active (the most recent update was last October). While the project is somewhat done, they're still pushing for compatibility and development in open tools like Fontforge. If you need your font to be reliable, you can't go wrong with GNU Unifont even though it lacks a distinct zero.