Check out Scribus!

Scribus is an Open Source program that brings professional Layout to Linux/UNIX, Mac OS, OS/2 Warp 4/eCom Station and Windows desktop with a combination of press-ready output and new approaches to page design.

Underneath a modern and user-friendly interface, Scribus supports professional publishing features, such as color separations, CMYK and Spot Color support, ICC color management, and versatile PDF creation.

Check out Gimp!

GIMP is an acronym for GNU Image Manipulation Program. It is a freely distributed program for tasks such as photo retouching, image composition and image authoring.

It has many capabilities. It can be used as a simple paint program, an expert quality photo retouching program, an online batch processing system, a mass production image renderer, an image format converter, etc.

Adobe InDesign can give you total creative freedom and some practice in using an industry-standard design tool, but can be overwhelming if you have never used an Adobe Creative Cloud product before. Here are some resources to help you get started:

• Getting your free or discount license from the Illinois WebStore
• Adobe InDesign Help (including video and text tutorials)
• If using images or graphics created outside of InDesign, remember to embed images before saving so that the images are saved with your poster
• Using Adobe InDesign to Create Accessible PDF Documents