I have tried various apps for creating fonts, such as FontStruct and Fonty with mixed results. Some work better than others. FontStruct works well, though I find it tricky to make letters with lots of curves. Fonty works well, though when I tried to use the fonts on my computer, the letters do not display at all.
Yesterday I found Glyphr Studio, a free, web-based font design tool that works well and produces usable fonts. I worked out how to import graphics, which is easier than making all the letters from scratch, though a little convoluted, as you have to save each letter as a separate image, convert the images to SVG files, then import them and tweak them. Strangely they are inverted when they appear in Glyphr.
Anyway, I make a rough font for Laala, which requires more tweaking, but looks okay.
If you make fonts, what software, apps or websites do you use?