The first competition of the year in which you can participate is clearly the BASIC 10Liners competition for all 8bit computers with line oriented BASIC dialects. In 2011 and 2013 the contest was an internal competiton of the retro computer meeting NOMAM in Lübeck / Germany, but a lot of contributions came from all around the world in 2014 and only one was produced live on the meeting. So if you are able to develop a BASIC program for one of the allowed systems, you can submit your contribution (deadline 22nd April 2017):
- All 8bit computer systems
Authorized BASIC dialects:
- All line oriented BASIC dialects
You will find more information about the contest on the BASIC 10Liners competition homepage (scroll down for the english translation). You can also have a look at the results of the last year.