For a while, I've been looking for a font to suit the needs of a project I'm undertaking. I realize this isn't a Linux Question, but it is about open source in the form of freely licensed fonts so I can embed them in documents. Whatever I use has to be
1. Open source, preferably under the OFL
2. Clean, machined sans serif. It can still belong to the "Humanist" family as long as it's appropriately minimalistic. I'm shooting for near invisibility here.
3. Uppercase I and lowercase l are clearly differentiated.
4. Has to have a "light" or "thin" weight. (Opposite of boldface)
I keep running into fonts that are almost perfect, but have devastating flaws.

1. Helvetica Neue Light. This one is right out. I am NOT paying an absurd amount of money for something that is STILL insanely license encumbered after buying. The uppercase I (i) and lowercase l (L) are also not differentiated. As far as I can tell, they use the same glyph.

2. Arial. This one is ubiquitous and I might not need to embed it, but the only thing it has to recommend it is its similarity to Helvetica Neue. It doesn't have a "light" variant and, like the Helvetica family, it makes no distinction between uppercase I and lowercase l. Incidentally, that makes this post hard, because the default font for editing in LQ is Arial and I don't want to change it to anything else because Tahoma has problems on some systems and I don't like serifs.

3. Liberation/Nimbus/Open Sans. Open source, but the I and l are not differentiated. No "light" weight.

4. Tahoma. This is a great font. The I and l are easily differentiated. I would recommend it if you never need to communicate with Linux users. It is unavailable on many distros, license encumbered, and doesn't have a "light" variant.

5. Source Sans Pro. Open source, I and l are easily differentiated, has a "light" weight, but is a little too decorative.

6. Noto Sans. This is my current favorite font. I love every glyph and almost everything about it, but it doesn't have a "light" weight and the apache license 2.0 is unclear about whether I have to include a license declaration when embedding the font in a document. This font is so good I might be willing to let the "light" weight requirement go as a last resort.

Does anybody have suggestions about what I might use or clarifications about the Noto Sans license?
EDIT: Does anybody know what the default display font for LQ posts is?

Finding the right font is a tedious task, and one that can only be carried out by the one holding the requirements IMHO.

Have you simply googled for free/open source fonts? I have been searching for just the correct font various times, and the main problem was not finding fonts, but looking at every character to see if it would fit my requirements.

jlinkels

It seems to me like I would be able to get help of some kind. Three of my criteria are completely objective, (open source, differentiable I and l, "light" weight/style) so I thought people might be able to recommend some fonts they like personally that satisfy those (like Source Sans Pro). I only included the more subjective one (invisibility) for the sake of completeness, and so people would know that I am looking for a general purpose font, as opposed to one that is designed to have a distinct/unique look. Help understanding the Apache 2.0 as it applies to pdf and epub embedding wouldn't go amiss either.

As for searching: the overwhelming majority of open source fonts found by DuckDuckGo use the same glyph for I and l, and don't have "light" weight variants. I was hoping to get some advice on how to find those. I couldn't figure out any sort of search terms that can narrow down any of the other criteria, so I concluded I needed to get some suggestions from a human being. Even just some pointers in the direction of "light" fonts would be nice, so I can, in your words, "look... ...at every character to see if it would fit my requirements." ("every character" meaning I and l.)

Just a quick update: I carefully reviewed the Apache 2.0. The license must be included with a "source or object form" of the software. I don't think pdf or epub embedding qualifies as either, so Noto Sans is open for consideration.

Dejavu free fonts.

Many fonts from under sil license. the sil site has a list of fonts.

scribus.net site has a list of quality fonts.

Dejavu Sans includes an extra light version. It doesn't distinguish "I" and "l", but the answer to that is to install Fontforge and alter one or the other.

I have run into some LibreOffice weirdness with Source Sans Pro and it's looking like DejaVu might run into the same. LibreOffice does not package all variants, leaving out the Light variant while including Regular and ExtraLight. However, LibreOffice seems to keep its preinstalled fonts separate from the system and user fonts on my system, as my system font manager doesn't show Source Sans Pro unless I install it. A consequence probably related to this is that LibreOffice doesn't reliably recognize the Light form of Source Sans Pro. Even though there are twelve variants, LibreOffice will not display more than ten. The odd part is that they are not always the same ten variants; rather, which two are left out varies when I uninstall and reinstall the font family from the system. This implies to me that the problem is not with the font files themselves, but somewhere in LibreOffice. Even weirder is that LibreOffice recognizes many more variants for fonts not packaged with LibreOffice (Fira Sans by Mozilla has <<32>> variants. It's another really promising one.) I know this is a tangent from the main question, but does anybody have ideas about why this might happen? I can't reliably use nonstandard variants of DejaVu or Source Sans Pro until I can fix this. The problem only occurs in OSX; on Linux everything is fine.

Isocteur is my current favourite font (of the 700 or so I have installed, yeah yeah - I know!) but I have never really checked deeply to find out what license it is under.

Some places have it listed simply as "free", some as "free for personal use" and some as "unknown".

I think it might match your other criteria though. HTH.

Thanks for the suggestion! Isocteur is nice, and I might try it out, but it doesn't quite fit the criteria. It seems like it tries to have its own sci-fi-ish "look" rather than being an all-purpose typeface. It's very beautiful, but as body text it seems like it would get old after about 5 pages.

It is certainly thin, but that is the "Regular" weight. One reason I am looking for a font with a "Light" weight variant is that I would like to be able to use the same font at different sizes without varying the stroke width. Most normal fonts look boldface to me at large sizes regardless of whether they actually are. For example, my ideal combination would be Noto Sans for 11 point body text and Noto Sans Light for 26 point title. Unfortunately, Noto Sans Light does not exist.

The license is certainly important, as I will be using this font embedded in pdf/rtf/odt/epub, what have you.

I'd love to hear some of the best from the other 700!

Haha. Most of them are not very interesting - I have just sort of accumulated them over the years. Many are not English because I have an interest in a translation business so all the computers have to have a wider range of fonts than would be normal.

Many are just 'novelty'. I like to enter photo-manipulating contests from time to time and having the right font for example a Roman tablet or a page coming out of a dot-matrix printer or something that screams "1970s!" can add a nice detail.

Back on topic, perhaps Gentium Basic or Nakula might do for your needs?

Sorry, but both of those are serif fonts. At least, Nakula claims that all its latin glyphs are drawn from Nimbus Roman No9, which is a serif font. I'm looking for a sans-serif where the I and l are distinct, but all other glyphs are as vanilla as possible, so the font as a whole is nearly invisible to the reader. So far, only Helvetica Neue has accomplished that. I'm beginning to think that I'm going to need to design my own font...

is ARIAL available as open source for Latex/TeX?

Arial is mentioned in the original post as using the same glyph for I and l, and also for having no "Light" variant.

How about something like Futura Renner?

1,2&4 of your list are met and the uppercase I is shorter than the lowercase l.

Futura Renner at the Open Font Library

The lowercase g is appalling, but it's still a great suggestion! Thanks!

About the I and l thing; my brother spent about a quarter hour on one question in his Chemistry homework because he couldn't figure out how Cl4 (tetrachlorine) was possible. It turns out it isn't. He was looking at CI4 (Carbon Tetraiodide) and mistook it for the other because the I and l differed only in height. The I and l in FuturaRenner only differ in height, and therefore are not distinguishable if they are not in the same word or in directly consecutive words. I may be overemphasizing that a bit...

I probably just need to learn to use the drawing tools in FontForge and thoroughly abuse Source Sans Pro to make my own font. Is there any sort of "snap to grid" function like in Inkscape?
I only hope whatever I settle on doesn't run into that stupid LibreOffice bug. It's not just preinstalled fonts after all. Fira Sans (by Mozilla) has 32 variants but only 15 display in LibreOffice. Not always the same 15; just 15. Fira Sans is not a LibreOffice font, which means any font is potentially susceptible to this.