Program on FreeDOS with Bywater BASIC: 
In the early days of personal computing—from the late 1970s and through the 1980s—many people got their start with BASIC programming. BASIC was a universal programming language that came built into most personal computers, from Apple to IBM PCs.
When we started the FreeDOS Project in June 1994, it seemed natural that we should include an open source BASIC environment. I was excited to discover one already existed in Bywater BASIC.
read more: Opensource.com Jim Hall
Supporting Open Source.
Have you tried: Diving with Sharks?