Here is a simple DIY planner for 2026: 2026-DIY-Planner.pdf.
If you have access to a printer that can print on both sides of a piece of paper, you can print yourself a letter sized 2026 planner using this file. You can then hole punch the pages and put the planner in a binder.
To create this, I used an awk program to write PostScript for the main planner and ps2pdf to convert the PostScript into a PDF. The initial calendar pages came from a combination of another awk program and the cal program.
And here is a shorter pdf which provides monthly spreads for 2026 planning, again for printing out double sided and hole punching to put in a binder: 2026-Monthly-Planner.pdf.