Complex sentence: The tools were first developed by Hans Petter Jansson at Helix Code, later, several other Helix Code employees were involved, most notably José-María Celorio, Arturo Espinosa, and Tambet Ingo.
Split into simpler sentences: The tools were first developed by Hans Petter Jansson at Helix Code. Later, several other Helix Code employees were involved, most notably José-María Celorio, Arturo Espinosa, and Tambet Ingo.